JPH02212120A - Vacuum forming - Google Patents

Abstract

PURPOSE:To attach a cut sheet along a vacuum mold keeping almost its original wall thickness and consequently obtain a product, the skin material of which is uniform and the quality of which is stable, by a method wherein the unfastening and fastening devices of clip to be actuated is set be forehand by a controlling apparatus in response to the required cubic shape for the operation of the unfastening and fastening device of clip. CONSTITUTION:When a vacuum mold 8 is pushed up against a cut sheet 1 at a vacuum forming section FS, clips at the sites of the cut sheet 1 in opposedly contact with the upper step part, middle step part and the like of the mold are put in grip unfastened states in response to the difference in the height level of the cubic shape of the mold so as to avoid the application of large stretching stress to the sites by means of the actuating mechanisms of split attachments 5a-5e of an attachment device AD. The grip unfastened state or concretely the grip unfastening at both sides of the cut sheet, the grip unfastening at one side of the cut sheet or the like, and the sites under the above-mentioned state are determined in response to the shape in height of the mold so as to cope with the minimization of the change due to the stretching of the cut sheet by the pushing-up stress. By setting the actuation any one of cylinders in advance by a controlling apparatus in response to the cubic shape so as to unfasten the clips at the proper sites of the cut sheet at forming, the above-mentioned grip unfastening and fastening actions give freedom to the cut sheet.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a vacuum forming method particularly suitable for manufacturing thin skin materials for interior parts with three-dimensional structures with large height differences. This refers to the vacuum forming of skin materials suitable for interior parts of vehicles, aircraft, etc.

[Prior Art] In the conventional continuous vacuum forming method, a sheet is generally formed using a continuous vacuum forming machine having a sheet feeding device, a heating device, and a forming device.

First, a roll sheet that is formed into a sheet with a desired outer surface shape using a calender and wound up into a roll is cut into a predetermined length using a sheet feeding device to form a cut sheet. This cut sheet is fixed to a conveyor chain within the sheet feeding device.

Two of these conveyor chains are provided in parallel to the winding direction of the roll sheet, that is, the length direction of the cut sheet, and have a structure that can hold two sides of the cut sheet, respectively. These two conveyor chains move endlessly in parallel between the heating device and the forming device, and as soon as vacuum forming is completed, the next sheet is fed into the forming device and continuously vacuum formed.

That is, the sheet from the sheet feeding device is conveyed to the heating device, the sheet from the heating device is conveyed to the forming device, and after being conveyed from the sheet feeding device to the heating device, a new sheet is automatically fed from the rolled sheet, and, Products molded by the molding device are automatically demolded.

Therefore, the distance between the two transport chains is the same as the width of the sheet. In addition, in the molding equipment, between the two conveyor chains, a vacuum mold pushes down the sheet from above the sheet or pushes the sheet up from below the sheet, and after making the vacuum mold sufficiently air tight with the sheet, the vacuum mold is moved between the two conveyor chains. The product is obtained by pulling. That is, when this vacuum mold is pushed up or down, the sheet is stretched. Such a molding method that causes elongation is unsuitable for molding thin skin materials. Conventionally, various molding methods have been considered in consideration of these fluctuations. These vacuum forming methods can be roughly divided into straight
) molding and drape molding.

Straight molding, also called female molding, is a method of molding a three-dimensional product into the desired shape using an inverted concave mold.The thermoplastic sheet is clamped to a movable frame and then heated and softened. In this method, a vacuum is drawn between the contact between the female mold and the sheet, the sheet is attracted to the female mold, and the sheet is cooled to complete the molding.

Drape molding, also called male molding, is a method of molding three-dimensional products using a convex mold that has the same shape as the desired shape (with shrinkage rate added depending on the characteristics of the sheet), and is similar to the former. In this method, a thermoplastic sheet is clamped to a movable frame, heated, pre-stretched along the ridges of a male mold, and then vacuumed to form the mold.

In addition to these two basic molding methods, an auxiliary plug (p
There is a plug-assist molding method that combines a plug-assist (lug-assist), etc. Plug-assisted molding is a sheet thermoforming method that uses a simple female mold (male mold) and male plug (female plug). After preforming the heated sheet using the plug, the Alternatively, the sheet is brought into close contact with the female mold using vacuum and compressed air to complete the molding.

There is also an air slip (ALR-SLIP) molding method.

This air slip molding (air action molding) is a type of vacuum forming method that uses a male mold.The male mold is placed in a box, the sheet is clamped to the upper edge of the box, and the sheet is heated and softened, and compressed air is blown from below. When the male mold is pushed up from below while inflating into a hemispherical shape, an air traction is formed between the mold and the sheet, so the mold does not come into contact with the sheet until it reaches the top, so partial cooling does not occur and the molded product becomes at the corner. No parts will break.

At this point, a vacuum is applied to eliminate air tension, and the sheet is drawn into a mold and molded.

Also, reverse-draw
There is a molding method.

This reverse draw molding is a method of thermoforming using a female mold, in which a heated sheet is expanded upward using compressed air and then evacuated to form the product. can be made uniform.

There is also a plug assist reverse draw molding method. This is a thermoforming method in which a heated sheet is freely expanded using compressed air, then predrawn in the opposite direction using a plug, and then the forming is completed using a vacuum. It is used to produce large-sized deep drawn products. It will be done.

There is also a drape assist frame forming method.

This drape assist frame molding is a framework used when making several pieces using a male mold in thermoforming, and is made of thin wire or thick rods shaped to fit around the valley of the mold. , this frame is suspended above the sheet to be molded, and during molding, this assist frame is lowered and stretches the sheet to fit snugly into the mold. In this way, the formation of folds in the sheet between the ridges of the molds can be prevented and the spacing between the molds can be determined more accurately.

In addition, vacuum snapback (vacuum 5nap-
There is a molding method. This vacuum snapback forming is a modification of the vacuum forming method, in which a heated sheet is placed between a male plug and a vacuum box, a vacuum is first drawn from the bottom of the vacuum box, and the sheet is pre-stretched into a concave shape. Then, when the plug is pushed down and the vacuum is removed, the sheet snaps back onto the surface of the male plug. This method is suitable for deep drawn products.

As mentioned above, in addition to the conventional molding method that involves direct vacuuming, which has a large variation in wall thickness, consideration has also been given to using auxiliary means such as auxiliary plugs in order to spread the sheet uniformly. In cases other than the method in which the wall thickness is often varied by being deformed at once by direct vacuum action and along the mold, that is, when using an auxiliary device, stretching stress is applied directly to the sheet of initial thickness using an auxiliary plug, etc. The material is stretched in two stages and molded along the mold.

In other words, it is expanded to a required area by a stretching effect to a greater or lesser extent.

[Problems to be Solved by the Invention] As described above, in the conventional molding method, a roll sheet of thermoplastic plastic wound into a roll is cut into a required length using a sheet feeding device. Both sides of the cut sheet are fixed to a conveyor chain, and the cut sheet is transferred through a heating section to a forming section above a vacuum forming mold.The lower vacuum forming mold is pushed up against the cut sheet with both sides fixed, and vacuum is applied to form the product. It is something to do.

Therefore, the cut sheet of the molding material has a constant wall thickness, but when the cut sheet is pushed up with a vacuum forming mold, the amount of pushing up varies from part to part depending on the shape of the vacuum forming mold, so the elongation of the cut sheet also increases. As a result, the wall thickness of the product also varies greatly.

During this push-up, the stretching variation exerted on the cut sheet due to the pushing up of the high and low parts causes a larger variation in wall thickness than expected, and especially in the case of a thin wall, a high rate of defects such as breakage occurs. Therefore, it is necessary to find a means for dispersing stress to evenly distribute the fluctuating stress generated when pushing up a vacuum forming mold having a three-dimensional shape with a large difference in height.

[Means for solving the problem] As mentioned above, when pushing up a male vacuum forming mold with a large height difference, when pushing up towards a cut sheet of thermoplastic sheet, firstly, the high - [two-step part is cut] When the sheet is pushed up and stretched, the middle and lower sections touch each other in sequence, but when the upper section stretches the sheet, the stretching action also spreads to the middle and lower sections, especially near the upper section. It is essential to distribute the stretching stress. Therefore, the inventors have attempted to disperse the stress by improving the clip mechanism of the cut sheet clip of the conveyance chain.

That is, it has been found that suitable stress distribution can be obtained by dividing the attachment device for fixing the clip into a large number of sections and unpacking and unpacking the clip in each section. To unpack and unpack this clip,
This is done by opening/closing devices such as cylinders attached to individual splitting attachments. In addition, the operation of the clip opening/closing device can be done by setting in advance which opening/closing device to operate in the control device according to the required three-dimensional shape, so that the appropriate part of the cut sheet can be selected during molding. It can be unpacked and set free. Further, the opening/closing operation can be performed in an appropriate manner, such as unpacking both sides of the cut sheet, unpacking one side, or alternately unpacking one side.

In this way, after dispersing the stress during thrusting,
When the cut sheet is gripped with a clip, the cut sheet is attached to the vacuum forming mold in a state close to its original thickness. In this attached state, vacuum suction is performed to completely follow the shape of the mold.

Alternatively, when performing vacuum operation while attached to a vacuum forming mold, if the shape is stretched to a large degree due to further contact, use the attached clip to clip the necessary part when vacuuming. The operation of releasing the stress is handled in the same way as when dispersing the stress.

In other words, in the case where the cut sheet is attached to the vacuum forming mold as described above, if the degree of crimp of the cut sheet to the mold is insufficient, unpack the clip of the dividing attachment in that area and attach it freely to the cut sheet. Apply vacuum suction by applying
After correcting the degree of creepage, the clip is further unpacked and vacuum forming is performed to complete the vacuum forming.

Note that a more detailed explanation will be given later based on the drawings of the embodiment.

[Function] The vacuum forming method operated as described above appropriately distributes stress in response to the magnitude of stress that changes the wall thickness due to the thrust of the vacuum forming mold against the cut sheet of material supplied to the vacuum forming mold. Therefore, it acts to suppress variations in the original thickness of the cut sheet. Therefore, since a thin outer skin material with less variation in wall thickness can be obtained, there is no need to increase the original thickness of the cut sheet of the supplied material in anticipation of fluctuations, and a suitable and excellent outer skin material can be obtained with a thin supplied material. wood is obtained.

[Example] Next, a conventional vacuum forming method and a vacuum forming method of the present invention will be compared with each other based on illustrative drawings.

FIG. 3 is a schematic diagram of the conventional vacuum forming method, showing the state of the conveyor chain, the vacuum forming mold, and the molding section above it.

FIG. 4 is a schematic diagram showing the spread state of a fixed cut sheet and a vacuum forming mold when they come into contact with each other in a conventional vacuum forming method.

An example of the conventional vacuum forming method is as shown in FIGS. 3 and 4, in which the cut sheet 1 is pierced through a pin 10 provided on a conveyance chain 9 and conveyed, and the attachment 11 of the forming section FS is attached to the pin 10. Cover and fix the cut sheet 1 (see Figure 4).

In this state, the vacuum forming mold 8 is raised and the cut sheet 1 is
The two are brought into contact with each other in a raised state, and vacuum formed by a vacuum drawing operation to obtain the outer skin material.

Since the cut sheet 1 of this conventional example is fixed to the conveyor chain 9, it is stretched and spread as the thickness changes as the die is pushed up (see FIG. 4).

Fig. 1 is a schematic diagram of the vacuum forming method of this invention, and Fig. 2 is a schematic diagram of the vacuum forming method of this invention.
Unpacking the clip 3 of the conveyor chain that grips the cut sheet,
It is a schematic diagram showing unpacking.

As shown in the figure, 1 is a cut sheet that is a thermoplastic sheet molding material, 2 is a conveyance chain that conveys the cut sheet, 3 is a clip provided on the conveyance chain 2, and 4 is a roller set on the top of the clip. The cut sheet 1 is held by a clip 3, and while being transferred to the forming section FS, it is heated by an infrared heating device or the like to an appropriate forming temperature for the thermoplastic sheet, and then transferred to the forming section FS. The cut sheet 1 is held by a clip 3 and placed in a vacuum forming mold 8.
When the clip 3 is transferred to the upper molding section FS, the clip 3 is fixed by the attachment device AD (see FIG. 2). The attachment device AD for fixing the clip 3 is composed of a dividing attachment 5 and a cylinder 6 of an opening/closing device, and the dividing attachment 5 is divided into a large number of sections corresponding to the length of the cut sheet. The division is performed in opposing positions to the conveyor chain 2 on both sides, for example, the division attachments 5 are 5a, 5b.

It is divided into 5c, 5d, 5e, etc., and an opening/closing device such as a cylinder 6 for unpacking and unpacking the clip 3 is provided for each divided attachment (5a, 5b, 5cφ hall).

In this opening/closing device, as shown in FIG. 2, split attachments 5 (numbers 5a, 5b, etc.) are connected at a fulcrum 7 so as to rotate freely, and are also connected to a rod of a cylinder 6 at the fulcrum 7. The rollers 4 set on the clips 3 are rotated about the fulcrum 7 by the stroke of the cylinder, thereby releasing the held cut sheet 1 and setting it in a free state. That is, the cylinder rod is in the extended state to put the clip in the unpacked state, and the rod is in the pulled state to put the clip in the unpacked state.

By the operating mechanism of the split attachment 5 of this attachment device AD, when the vacuum forming mold 8 is pushed up onto the cut sheet 1 in the vacuum forming section FS, the upper stage is , the clips at the opposing portions of the cut sheet 1, such as the middle section, are unpacked so that no large stretching stress is applied to those portions. This open grasping state is handled by determining the location and its open grasping state, such as unpacking on both sides, unpacking on one side, etc., depending on the height and low shape, and minimizing fluctuations due to stretching of the cut sheet due to uplift stress. do. This unpacking and unpacking operation can be done by setting in advance which cylinder to operate in the control device according to the three-dimensional shape, and by releasing the clips at the appropriate part of the cut sheet during molding, it is possible to freely can give sex.

In this way, when the vacuum forming die 8 is pushed up, the cut sheet 1 is placed on the vacuum forming die 8 in a state close to its original thickness, and when the cut sheet 1 is grabbed with a clip in this state, the cut sheet is It is attached to the mold 8. When vacuum suction is applied in this state, the mold is completely molded into the mold shape. Note that vacuum forming can also be performed continuously by setting the cut sheet to be conveyed at the same time as the forming is completed and sent out.

[Effects of the Invention] As explained above, the vacuum forming method of the present invention performs vacuum forming in a state close to the original thickness of the cut sheet of the forming material, so there is little variation in wall thickness and there is no large height difference. It is possible to manufacture products of uniform and stable quality using thin skin materials for three-dimensional interior parts with high efficiency.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the vacuum forming method of this invention, and Fig. 2 is a schematic diagram of the vacuum forming method of this invention.
Figure 3 is a schematic diagram of the unpacking and unpacking operation of the clip of the conveyance chain of the present invention, Figure 3 is a schematic diagram of the conventional vacuum forming method, and Figure 4 is a diagram showing the conventional fixed cut sheet and the vacuum forming mold. FIG. 2 is a schematic diagram showing the state of development of time. 1... Cut sheet 2... Conveyance chain 3...
・Clip 5 (5a, 5b, 5c, 5d, 5e) - Split attachment 8... Vacuum forming mold FS... Molding part AD... Split attachment device

Claims (2)

[Claims] (1) In vacuum forming thermoplastic sheets, cut sheets cut to the required width and length are fed to a conveyor chain, and during conveyance, a heating device such as an infrared ray is used to properly form the thermoplastic cut sheets. The cut sheet is heated to a high temperature and transferred to the molding section, and the transported cut sheet is held in a fixed state by a dividing attachment that is divided into many sections in the forming section, and the upper and middle sections of the height difference in the shape of the vacuum molding die are heated. Open and grip the clips on both sides or one side of the dividing attachment at the corresponding part of the section, give the cut sheet the necessary degree of freedom, push up the vacuum forming mold, attach the cut sheet to the vacuum forming mold, and open and grip the clips. A vacuum forming method characterized by vacuum forming by holding the attachment clip closed. (2) Give the cut sheet the necessary degree of freedom, push up the vacuum forming mold, attach the cut sheet to the vacuum forming mold, and when closing and grasping the split attachment clip, the cut sheet does not have sufficient contact with the mold. In such a case, open and hold the clip of the splitting attachment at that part, give the cut sheet a degree of freedom, apply vacuum suction, correct the degree of crimp, and then close the clip again and apply further suction to apply vacuum. The vacuum forming method according to claim 1, characterized in that forming is completed.