CN216607786U

CN216607786U - Workpiece clamping unit

Info

Publication number: CN216607786U
Application number: CN202123172903.2U
Authority: CN
Inventors: 王建忠; 曾丽娜; 刘雁清; 刘定基; 吴葛铭; 杨漾; 贺礼
Original assignee: Hunan Zhongnan Intelligent Laser Technology Co ltd
Current assignee: Hunan Zhongnan Intelligent Laser Technology Co ltd
Priority date: 2021-12-15
Filing date: 2021-12-15
Publication date: 2022-05-27
Anticipated expiration: 2031-12-15

Abstract

The clamping unit of the workpiece comprises a bottom plate assembly, a first side plate assembly, a second side plate assembly, an upper plate assembly, a first position limiting piece and a second limiting piece; the bottom plate assembly comprises a bottom plate, and a guide rod pressing assembly and a positioning pin which are arranged on the bottom plate, wherein the positioning pin is matched with a positioning hole on a workpiece; the first position limiting piece and the second limiting piece are respectively fixed at two ends of the bottom plate; the upper plate assembly comprises an upper plate and a guide rod pressing assembly arranged on the upper plate, the first side plate assembly comprises a first side plate and a guide rod pressing assembly arranged on the first side plate, the second side plate assembly comprises a second side plate and a guide rod pressing assembly arranged on the second side plate, the bottom plate, the upper plate, the first side plate, the second side plate, the first position limiting part and the second position limiting part enclose a cube with a containing cavity, and the upper plate is placed on the top ends of the first side plate and the second side plate. The clamping unit of the workpiece clamps the workpiece stably and reliably, displacement does not occur during welding, and reliability of welding quality is guaranteed.

Description

Workpiece clamping unit

Technical Field

The utility model belongs to the technical field of machinery, and particularly relates to a workpiece clamping unit.

Background

The outer coating piece of the engine exhaust pipe casting is used for isolating heat overflow and protecting the exhaust pipe casting from rusting. Welding of an engine exhaust pipe casting outer coating piece is a novel process, and a heat insulation material and a stainless steel metal sheet are coated outside an engine exhaust pipe to be welded. Because the shape of an engine exhaust pipe casting is complex, the outer cladding heat-insulating material and the stainless steel sheet are difficult to clamp and position, and the outer cladding heat-insulating material and the stainless steel sheet are easy to clamp loosely during welding, so that the technical problems of more welding spots, low welding efficiency, high welding cost, unstable welding quality, easy occurrence of welding defects, incapability of meeting the requirements of batch production and the like are caused. For effectively improving production efficiency and welding quality stability, the clamping unit of a workpiece needs to be researched and developed urgently at present, so that the complex appearance of a casting is adapted, the position of each welding line is attached, and the welding stability and the welding quality reliability are ensured.

The utility model has the following contents:

the utility model aims to provide a workpiece clamping unit, which effectively solves the problems of difficult clamping and positioning and the like in the prior art, adapts to the complex appearance of a casting, and ensures the position fitting of each welding line, thereby ensuring the welding stability and the reliability of the welding quality.

In order to achieve the purpose, the utility model adopts the following technical scheme:

a clamping unit of a workpiece is used for clamping and positioning an outer casting cladding piece of a casting and comprises a bottom plate component, a first side plate component, a second side plate component, an upper plate component, a first position limiting piece and a second position limiting piece; the bottom plate assembly comprises a bottom plate, and a guide rod pressing assembly and a positioning pin which are arranged on the bottom plate, wherein the positioning pin is used for matching with a positioning hole in a workpiece and fixing the workpiece; the first position limiting part and the second limiting part are respectively fixed at two ends of the bottom plate; the upper plate subassembly includes the upper plate and installs the guide arm of upper plate compresses tightly the subassembly, first curb plate subassembly includes first curb plate and installs the guide arm of first curb plate compresses tightly the subassembly, second curb plate subassembly includes the second curb plate and installs the guide arm of second curb plate compresses tightly the subassembly, the bottom plate the upper plate first curb plate the second curb plate first locating part and second locating part enclose to close and form and have the cube that holds the chamber, the upper plate rest in first curb plate with the top of second curb plate.

On the basis of the scheme, in another improved scheme, the guide rod pressing assembly comprises a pressing rod, a spring and a pressing block; the bottom plate the upper plate the first curb plate and the second curb plate have all been seted up connecting hole and spring chamber, the connecting hole with spring chamber intercommunication, placed in the spring chamber the spring, the one end of depression bar is passed the connecting hole with behind the spring with the compact heap is connected, the compact heap is arranged in hold the inside in chamber, the compact heap is used for compressing tightly and places hold the workpiece surface in the intracavity. In order to adapt to the complex appearance of the casting outer cladding piece, the pressing block in contact with the workpiece is in a copying design, the surface of the pressing block in contact with the workpiece is attached to the appearance of the workpiece, and the pressing block is tightly attached to the surface of the workpiece by the aid of elasticity of the spring.

On the basis of the above scheme, in another improved scheme, one end of the spring is placed in the spring cavity, and the other end of the spring is tightly attached to the surface of the pressing block, when the spring is in an uncompressed state, a gap exists between the pressing block and the bottom plate or the upper plate or the first side plate or the second side plate, and the pressing block presses the surface of the workpiece placed in the accommodating cavity under the elastic force of the spring.

On the basis of the scheme, in another improved scheme, a hollow connecting sleeve is fixed in the connecting hole, and the pressure rod penetrates through the connecting sleeve and is in clearance fit with the connecting sleeve. Adopt the copper sheathing as adapter sleeve in this embodiment, can provide the direction for the depression bar removes like this, crooked when avoiding the depression bar to remove.

On the basis of the scheme, in another improved scheme, the guide rod pressing assembly further comprises a nut, and the nut is in threaded connection with the end, far away from the pressing block, of the pressing rod.

On the basis of the scheme, in another improved scheme, the bottom plate, the first side plate, the second side plate and the upper plate are provided with a plurality of groups of guide rod pressing assemblies.

On the basis of the scheme, in another improved scheme, the device further comprises a side plate driving assembly for driving the first side plate and the second side plate to be close to or far away from the bottom plate, wherein the side plate driving assembly comprises a gear, two racks, two guide rails, two sliding blocks, two L-shaped connecting pieces and a power cylinder; the axle of gear is fixed on the bottom plate, two rack parallel mount be in the both sides of gear, and two the rack with gear engagement, the guide rail is fixed the bottom surface of bottom plate, the slider with the guide rail is mutually supported, two the horizontal part of L type connecting piece respectively with two the bottom fixed connection of slider, two the vertical portion of L type connecting piece respectively with first curb plate with second curb plate fixed connection, two the rack is fixed the horizontal part bottom surface of L type connecting piece, power cylinder pass through the cylinder connecting block with L type connecting piece is connected, power cylinder is used for driving one of them L type connecting piece horizontal migration. Because the gear is meshed with the two racks simultaneously, the moving directions of the two racks are opposite. When the power cylinder drives one of the L-shaped connecting pieces and the rack to move, the sliding block fixedly connected with the L-shaped connecting pieces moves along the guide rail and the rack drives the gear to rotate, so that the other rack is driven to move in the reverse direction through the gear rotation, and the other L-shaped connecting piece moves in the reverse direction. Therefore, the first side plate and the second side plate are driven to move simultaneously through the two L-shaped connecting pieces, and the first side plate and the second side plate are close to or far away from the bottom plate simultaneously.

On the basis of the scheme, in another improved scheme, the number of the side plate driving assemblies is two, and the two groups of side plate driving assemblies are symmetrically arranged on the bottom plate.

On the basis of the above scheme, in another improved scheme, the pressing device further comprises an upper plate pressing assembly respectively arranged beside the first limiting part or the second limiting part, the upper plate pressing assembly comprises an air cylinder mounting seat, a pressing air cylinder and a pressing arm, the air cylinder mounting seat is fixed on the first limiting part or the second limiting part, the pressing air cylinder is fixed on the air cylinder mounting seat, one end of the pressing arm is connected with an output end of the pressing air cylinder, and the other end of the pressing arm presses the upper plate under the action of the pressing air cylinder.

On the basis of the scheme, in another improved scheme, through holes for welding are formed in the bottom plate, the first side plate and the second side plate.

The utility model has at least the following beneficial effects:

according to the workpiece clamping unit, the workpiece of the external casting coating piece is positioned through the positioning pin, the workpiece is pressed from all directions through the guide rod pressing assemblies on the upper plate, the bottom plate, the first side plate and the second side plate, and the workpiece is guaranteed to be clamped stably and reliably, so that displacement is not prone to occurring between the coating heat-insulating material and the stainless steel sheet when the external casting coating piece is welded, and therefore welding stability and welding quality reliability are guaranteed.

Drawings

FIG. 1 is a front view of a workpiece clamping unit according to one embodiment of the present invention;

FIG. 2 is a cross-sectional view taken at A of FIG. 1, illustrating the construction of the guide bar hold down assembly;

FIG. 3 is a schematic perspective view of a clamping unit for clamping a workpiece according to another embodiment of the present invention;

FIG. 4 is a top view of FIG. 3;

FIG. 5 is a schematic view of another perspective of the clamping unit of the workpiece shown in FIG. 3;

fig. 6 is a schematic view of the structure of the workpiece of fig. 3 when the clamping unit is horizontally disposed.

Reference numerals:

1-bottom plate assembly 2-side plate driving assembly 3-first side plate assembly

4-first position limiting part 5-upper plate pressing component 6-upper plate component

7-second stop 8-second side plate assembly

1.1-bottom plate 1.2-guide rod pressing component 1.3-positioning pin

2.1-gear 2.2-guide rail 2.3-L-shaped connecting piece

2.4-power cylinder 2.5-rack 2.6-cylinder connecting block

2.7-slide block 3.1-first side plate 5.1-cylinder mounting seat

5.2-pressing cylinder 5.3-pressing arm 6.1-upper plate

101-pressure rod 102-nut 103-copper sleeve

104-spring 105-pressing block

Detailed Description

The following preferred embodiments of the present invention are provided to aid in a further understanding of the utility model. It should be understood by those skilled in the art that the description of the embodiments of the present invention is by way of example only, and not by way of limitation.

Referring to the schematic drawings of fig. 1 to 2, the clamping unit of the workpiece in an embodiment of the present invention is used for clamping and positioning an outer casting cladding, and includes a bottom plate assembly 1, a first side plate assembly 3, a second side plate assembly 8, an upper plate assembly 6, a first position limiting member 4, and a second position limiting member 7; the bottom plate component 1 comprises a bottom plate 1.1, and a guide rod pressing component 1.2 and a positioning pin 1.3 which are arranged on the bottom plate 1.1, wherein the positioning pin 1.3 is used for matching with a positioning hole on a workpiece and fixing the workpiece; the first position limiting part 4 and the second position limiting part 7 are respectively fixed at the right end part and the left end part of the bottom plate 1.1; the upper plate assembly 6 comprises an upper plate 6.1 and a guide rod pressing assembly 1.2 installed on the upper plate 6.1, the first side plate assembly 3 comprises a first side plate 3.1 and a guide rod pressing assembly 1.2 installed on the first side plate 3.1, the second side plate assembly 8 comprises a second side plate and a guide rod pressing assembly 1.2 installed on the second side plate, the bottom plate 1.1, the upper plate 6.1, the first side plate 3.1, the second side plate, the first limiting part 4 and the second limiting part 7 are enclosed to form a cube with a containing cavity, and the upper plate 6.1 is placed on the top ends of the first side plate 3.1 and the second side plate.

The shape of an engine exhaust pipe casting is complex, in order to ensure that an outer coating heat-insulating material and a stainless steel sheet are reliably clamped and fixed during welding, a workpiece is firstly placed in an accommodating cavity, and then the workpiece is inserted into a reserved positioning hole on the workpiece through a positioning pin 1.3 on a bottom plate 1.1 to realize positioning of the workpiece. Through setting up curb plate drive assembly 2, drive first curb plate 3.1 and second curb plate and be close to or keep away from bottom plate 1.1, guarantee first curb plate 3.1 and the side of second curb plate close to bottom plate 1.1 when the welding. Because the guide rod pressing assemblies 1.2 are arranged on the bottom plate assembly 1, the first side plate assembly 3, the second side plate assembly 8 and the upper plate assembly 6, the corresponding guide rod pressing assemblies 1.2 are arranged on two sides of each welding seam according to the positions of the welding seams, and the surfaces of workpieces are pressed in multiple directions through the guide rod pressing assemblies 1.2. The first position limiting part 4 and the second position limiting part 7 are designed in a copying mode for adapting to the complex appearance of a casting, the surface of the guide rod pressing component 1.2 which is in contact with a workpiece is pressed, the surface of the workpiece is pressed, and the position of each welding line of the heat-insulating material and the stainless steel sheet which are coated outside is attached, so that the welding stability and the welding quality reliability are guaranteed.

With reference to the illustrations of fig. 1 and 2, on the basis of the above-described embodiment, in a further modified embodiment, the guide rod pressing assembly 1.2 comprises a pressing rod 101, a spring 104 and a pressing block 105; connecting holes and spring cavities are formed in the bottom plate 1.1, the upper plate 6.1, the first side plate 3.1 and the second side plate, the connecting holes are communicated with the spring cavities, springs 104 are placed in the spring cavities, one end of the pressing rod 101 penetrates through the connecting holes and the springs 104 and then is connected with the pressing block 105, the pressing block 105 is placed in the cavity, and the pressing block 105 is used for pressing the surface of a workpiece placed in the cavity. In order to adapt to the complex appearance of the casting outer cladding piece, the pressing block 105 in contact with the workpiece is in a copying design, the surface of the pressing block 105 in contact with the workpiece is attached to the appearance of the workpiece, the pressing block 105 is tightly attached to the surface of the workpiece by the aid of elasticity of the spring 104, and the workpiece is guaranteed not to be displaced in the welding process.

Referring to the schematic illustration of fig. 2, on the basis of the above embodiment, in another modified embodiment, one end of the spring 104 is placed in the spring cavity, and the other end of the spring is tightly attached to the surface of the pressing block 105, when the spring 104 is in an uncompressed state, a gap exists between the pressing block 105 and the bottom plate 1.1 or the upper plate 6.1 or the first side plate 3.1 or the second side plate, and the pressing block 105 presses the surface of the workpiece placed in the accommodating cavity under the elastic force of the spring 104. With the arrangement, on one hand, the guide rod pressing assembly 1.2 can automatically adapt to workpieces within a certain size range, and on the other hand, the pressing block 105 can be guaranteed to be pressed on the surface of the workpiece by the aid of the telescopic size of the spring 104.

Continuing with the schematic illustration of FIG. 2, in a further modified embodiment, based on the above embodiment, a hollow adapter sleeve is fixed in the connecting hole, and the pressure rod 101 passes through the adapter sleeve and is in clearance fit with the adapter sleeve. In the embodiment, the copper sleeve 103 is used as a connecting sleeve, so that the movement of the pressure lever 101 can be guided, and the pressure lever 101 is prevented from being inclined when moving.

Continuing with the schematic illustration of fig. 2, in a further modified embodiment, based on the above embodiment, the guide bar hold-down assembly 1.2 further comprises a nut 102, and the nut 102 is screwed to the end of the pressure bar 101 remote from the hold-down block 105. Since the pressing rod 101 penetrates through the bottom plate 1.1 or the first side plate 3.1 or the second side plate or the bottom plate 1.1, and is not fixedly connected, the position of the pressing rod 101 can be ensured to be relatively fixed by arranging the nut 102.

Referring to the schematic drawings of fig. 3 and 4, on the basis of the above embodiment, in another modified embodiment, the bottom plate 1.1, the first side plate 3.1, the second side plate and the upper plate 6.1 are all provided with a plurality of sets of guide rod pressing assemblies 1.2. Therefore, workpieces placed in the accommodating cavity can be guaranteed to be compressed from top to bottom and from front to back, so that the positions of all welding seams are attached during welding, and the welding quality is guaranteed.

Referring to the schematic drawings of fig. 1 and fig. 3 to fig. 6, on the basis of the above embodiment, in another modified embodiment, the workpiece clamping unit further includes a side plate driving assembly 2 for driving the first side plate 3.1 and the second side plate to approach or depart from the bottom plate 1.1, and the side plate driving assembly 2 includes a gear 2.1, two racks 2.5, two guide rails 2.2, two sliders 2.7, two L-shaped connectors 2.3 and a power cylinder 2.4; the axle of gear 2.1 is fixed on bottom plate 1.1, two rack 2.5 parallel mount are in gear 2.1's both sides, and two rack 2.5 and gear 2.1 mesh, guide rail 2.2 is fixed in bottom surface of bottom plate 1.1, slider 2.7 and guide rail 2.2 mutually support, the horizontal part of two L type connecting pieces 2.3 respectively with the bottom fixed connection of two slider 2.7, the vertical portion of two L type connecting pieces 2.3 respectively with first curb plate 3.1 and second curb plate fixed connection, two rack 2.5 are fixed in the horizontal part bottom surface of L type connecting piece 2.3, power cylinder 2.4 is connected with L type connecting piece 2.3 through cylinder connecting block 2.6, power cylinder 2.4 is used for driving one of them L type connecting piece 2.3 horizontal migration. Since the gear 2.1 meshes with both racks 2.5 simultaneously, the direction of movement of both racks 2.5 is opposite. When the power cylinder 2.4 drives one of the L-shaped connecting pieces 2.3 and the rack 2.5 to move, the sliding block 2.7 fixedly connected with the L-shaped connecting piece 2.3 moves along the guide rail 2.2 and the rack 2.5 drives the gear 2.1 to rotate, so that the gear 2.1 rotates to drive the other rack 2.5 to move in the opposite direction, and the other L-shaped connecting piece 2.3 moves in the opposite direction. Thus, the first side plate 3.1 and the second side plate are driven to move simultaneously through the two L-shaped connecting pieces 2.3, and the first side plate 3.1 and the second side plate are close to or far away from the bottom plate 1.1 simultaneously.

Referring to the schematic diagrams of fig. 5 and fig. 6, on the basis of the above embodiment, in another modified embodiment, the number of the side plate driving assemblies 2 is two, the two side plate driving assemblies 2 are symmetrically arranged on the bottom plate 1.1, and the L-shaped connecting pieces 2.3 of the two side plate driving assemblies 2 are symmetrically arranged on the first side plate 3.1 and the second side plate. Set up like this, first curb plate 3.1 and second curb plate all are connected with two sets of curb plate drive assembly 2, can guarantee that the both ends of first curb plate 3.1 and second curb plate are close to or keep away from bottom plate 1.1 simultaneously. When the power cylinder 2.4 drives the first side plate 3.1 and the second side plate to cling to the bottom plate 1.1, the two ends of the first side plate 3.1 and the second side plate cling to the first limiting part 4 and the second limiting part 7. Under the action of the power cylinder 2.4, a cubic structure with a containing cavity is formed between the first side plate 3.1 and the second side plate, the bottom plate 1.1 and the upper plate 6.1 in a close fit manner.

Referring to the schematic diagrams of fig. 3 to fig. 6, on the basis of the above embodiment, in another modified embodiment, the present invention further includes two upper plate 6.1 pressing assemblies 5 respectively disposed beside the first position limiting member 4 and the second limiting member 7, where each of the upper plate 6.1 pressing assemblies 5 includes a cylinder mounting base 5.1, a pressing cylinder 5.2, and a pressing arm 5.3, the two cylinder mounting bases 5.1 are respectively fixed on the first position limiting member 4 or the second limiting member 7, the pressing cylinder 5.2 is fixed on the cylinder mounting base 5.1, one end of the pressing arm 5.3 is connected to an output end of the pressing cylinder 5.2, and the other end of the pressing arm 5.3 exceeds the first position limiting member 4 or the second limiting member 7 and rests on the upper plate 6.1. Through setting up upper plate 6.1 and compressing tightly subassembly 5, realize the reliable jam in first locating part 4 and second locating part 7 in the both ends of upper plate 6.1. When a workpiece needs to be placed in or taken out of the accommodating cavity, the output end of the pressing cylinder 5.2 drives the pressing arm 5.3 to be opened, the upper plate 6.1 is taken down, and then the workpiece is placed in or taken out. When a workpiece needs to be pressed, the upper plate 6.1 is placed on the first limiting part 4 and the second limiting part 7, and then the pressing cylinder 5.2 is started to drive the pressing arm 5.3 to press the upper plate 6.1.

Referring to the schematic diagrams of fig. 1 and fig. 3 to fig. 6, on the basis of the above embodiment, in another modified embodiment, through holes for welding are formed in the bottom plate 1.1, the first side plate 3.1 and the second side plate. With the arrangement, when the workpiece is fixed in the accommodating cavity through the positioning pin 1.3 and the guide rod pressing assembly 1.2, the welding gun welds the workpiece through the through hole.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present application and not for limiting the protection scope thereof, and although the present application is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: numerous variations, modifications, and equivalents will occur to those skilled in the art upon reading the present application and are within the scope of the claims as issued or as granted.

Claims

1. A clamping unit of a workpiece is used for clamping and positioning an outer casting cladding piece of a casting and is characterized by comprising a bottom plate component, a first side plate component, a second side plate component, an upper plate component, a first position limiting piece and a second position limiting piece; the bottom plate assembly comprises a bottom plate, a guide rod pressing assembly and a positioning pin, wherein the guide rod pressing assembly and the positioning pin are installed on the bottom plate, and the positioning pin is used for being matched with a positioning hole in a workpiece and fixing the workpiece; the first position limiting part and the second limiting part are respectively fixed at two ends of the bottom plate; the upper plate subassembly includes the upper plate and installs the guide arm of upper plate compresses tightly the subassembly, first curb plate subassembly includes first curb plate and installs the guide arm of first curb plate compresses tightly the subassembly, the second curb plate subassembly includes the second curb plate and installs the guide arm of second curb plate compresses tightly the subassembly, the bottom plate the upper plate first curb plate the second curb plate first locating part and second locating part enclose to close and form the cube that has the chamber of holding, the upper plate rest in first curb plate with the top of second curb plate.

2. The workpiece clamping unit of claim 1, wherein the guide rod clamping assembly comprises a compression bar, a spring and a clamping block; the bottom plate the upper plate the first curb plate and the second curb plate have all been seted up connecting hole and spring chamber, the connecting hole with spring chamber intercommunication, placed in the spring chamber the spring, the one end of depression bar is passed the connecting hole with behind the spring with the compact heap is connected, the compact heap is arranged in hold the inside in chamber.

3. The workpiece clamping unit of claim 2, wherein one end of the spring is arranged in the spring cavity, and the other end of the spring is tightly attached to the surface of the pressing block.

4. A workpiece clamping unit as claimed in claim 3 wherein a hollow coupling sleeve is secured within the coupling bore, the compression bar passing through the coupling sleeve with a clearance fit.

5. The workpiece clamping unit of claim 4, wherein the guide bar compression assembly further comprises a nut threadably coupled to an end of the compression bar distal from the compression block.

6. The workpiece clamping unit of claim 5, wherein said base plate, said first side plate, said second side plate and said upper plate are each provided with a plurality of sets of said guide bar hold down assemblies.

7. The workpiece clamping unit of any one of claims 1-6, further comprising a side plate drive assembly for moving the first and second side plates toward or away from the base plate; the side plate driving assembly comprises a gear, two racks, two guide rails, two sliding blocks, two L-shaped connecting pieces and a power cylinder; the axle of gear is fixed on the bottom plate, two rack parallel mount is in the both sides of gear, and two the rack with gear engagement, the guide rail is fixed the bottom surface of bottom plate, the slider with the guide rail is mutually supported, two the horizontal part of L type connecting piece respectively with two the bottom fixed connection of slider, two the vertical portion of L type connecting piece respectively with first curb plate with second curb plate fixed connection, two the rack is fixed the horizontal part bottom surface of L type connecting piece, power cylinder pass through the cylinder connecting block with L type connecting piece is connected, power cylinder is used for driving one of them L type connecting piece horizontal migration.

8. The workpiece clamping unit of claim 7, wherein the number of the side plate driving assemblies is two, and the two side plate driving assemblies are symmetrically arranged on the bottom plate.

9. The workpiece clamping unit according to claim 8, further comprising an upper plate pressing assembly disposed beside the first position limiting member or the second position limiting member, respectively, wherein the upper plate pressing assembly includes a cylinder mounting seat, a pressing cylinder and a pressing arm, the cylinder mounting seat is fixed to the first position limiting member or the second position limiting member, the pressing cylinder is fixed to the cylinder mounting seat, one end of the pressing arm is connected to an output end of the pressing cylinder, and the other end of the pressing arm presses the upper plate under the action of the pressing cylinder.

10. The workpiece clamping unit of claim 7, wherein the bottom plate, the first side plate and the second side plate are all provided with through holes for welding.