DE102020201407B4 - Process for producing a press-hardened and trimmed sheet metal part - Google Patents

Abstract

Method for producing a press-hardened and trimmed sheet metal part, with the steps:- Inserting a heated and austenitized sheet steel material (M) into a press-hardening tool (100) which has a die (110) and a punch (130);- Hot forming of the sheet steel material (M ) to form a sheet metal part, for which the press-hardening tool (100) performs a continuous closing movement (S), with the steel sheet material (M) being hot-formed by means of a spring-loaded hold-down device (120) belonging to the press-hardening tool (100), which presses the steel sheet material (M) against the Stamp (130) presses, is fixed to prevent slipping; - trimming of the shaped sheet metal part in the press-hardening tool (100) to produce an outer contour before the closing movement (S) reaches its bottom dead center (UT) and before the shaped sheet metal part is finished, wherein the steel sheet material (M) is still fixed by means of the blank holder (120); - final forming of the trimmed n Sheet metal part while the closing movement (S) is continued to its bottom dead center (BDC), with at least one outer cut surface (F) produced during trimming on the sheet metal part being further retracted during finish forming, and press hardening of the sheet metal part in the bottom dead center (BDC) of the closing movement (S);- opening the press-hardening tool (100) and removing the press-hardened and trimmed sheet metal part.

Description

The invention relates to a method for producing a press-hardened and trimmed shaped sheet metal part.

the EP 2 583 768 B1 Applicant describes a method for press hardening and cutting a steel sheet material, wherein a forming operation and a cutting operation are performed in one press stroke. The sheet steel material is heated to a temperature of more than 900°C before it is placed in the appropriately designed tool. Closing the tool causes the sheet steel material to be shaped, with the sheet steel material lying against actively cooled tool surfaces, which leads to hardening of the sheet steel material. To produce a defined outer contour, a cutting operation is then carried out in at least one section that extends steeply in relation to the working direction while still in the tool. The course of the cutting line lies outside the actively cooled tool surfaces and is therefore in sections in which the steel sheet material is not hardened or only very slightly hardened during the previous forming, with the steel sheet material being cut while it is still heated to between 600°C and 700°C.

• - Erwärmen des Metallwerkstücks auf eine erste Temperatur, insbesondere auf eine Austenitisierungstemperatur, und Positionieren des Metallwerkstücks zwischen den Matrizen (d. h. zwischen Matrize und Stempel) eines Warmumformwerkzeugs;
• - durch Zusammenfahren der Matrizen wird das Metallwerkstück nun umgeformt, insbesondere tiefgezogen;
• - nach Abschluss des Umformens wird mittels Schneidelementen eine Trennoperation ausgeführt, mit welcher ein Randbereich des Metallwerkstücks abgetrennt wird.

The closest DE 10 2006 040 224 A1 describes a method for hot forming a metal workpiece, with the steps:

• - Heating the metal workpiece to a first temperature, in particular to an austenitizing temperature, and positioning the metal workpiece between the dies (ie between the die and the punch) of a hot-forming tool;
• - By moving the matrices together, the metal workpiece is now formed, in particular deep-drawn;
• - After completion of the forming, a separating operation is carried out by means of cutting elements, with which an edge region of the metal workpiece is separated.

Forming and cutting are done quickly. In particular, the severing is substantially completed before the metal workpiece reaches a second, lower temperature at which its material has a significantly higher strength. However, it can also be provided that separation occurs towards the end of the forming.

The prior art is also referred to DE 10 2012 224 418 A1 , DE 10 2011 110 597 A1 , DE 10 2008 034 996 A1 and DE 10 2011 116 714 A1 as well as to the later published one DE 10 2018 215 545 A1 .

The invention is based on the object of providing a further advantageous method for producing a press-hardened and trimmed sheet metal part which does not have at least one disadvantage associated with the closest prior art or has it only to a reduced extent.

This object is achieved by the method according to the invention with the features of patent claim 1. Additional features result from the dependent patent claims, the following description and also the figures and drawings.

• - Einlegen eines zuvor auf Austenitisierungstemperatur (bspw. auf 860°C bis 950°C) erwärmten und dadurch austenitisierten Stahlblechmaterials, insbesondere in Form einer ebenen Stahlblechplatine, in das (geöffnete) Presshärtewerkzeug, wobei die Einlegetemperatur bevorzugt nur 650°C bis 850°C beträgt;
• - Warmumformen des Stahlblechmaterials bzw. der Stahlblechplatine zu einem Blechformteil, wozu das Presshärtewerkzeug eine kontinuierliche bzw. ununterbrochene Schließbewegung ausführt;
• - Beschneiden des Blechformteils im Presshärtewerkzeug zur Erzeugung einer Außenkontur, bevor die Schließbewegung ihren unteren Totpunkt erreicht;
• - Fertigformen des beschnittenen Blechformteils während die Schließbewegung bis in ihren unteren Totpunkt fortgesetzt wird und Presshärten des Blechformteils im unteren Totpunkt der Schließbewegung;
• - Öffnen des Presshärtewerkzeugs (durch eine Öffnungsbewegung) und Entnehmen des beschnittenen und pressgehärteten Blechformteils, wobei die gemittelte Entnahmetemperatur bevorzugt unter 200°C liegt.

The method according to the invention for producing a press-hardened and trimmed sheet metal part, in particular a body sheet metal component or an axle sheet metal component (for a motor vehicle), the production being carried out using a die and punch (in particular press-bound) press-hardening tool, comprises at least the following steps:

• - Insertion of a steel sheet material previously heated to the austenitization temperature (e.g. to 860°C to 950°C) and thus austenitized, in particular in the form of a flat sheet steel blank, into the (open) press-hardening tool, the insertion temperature preferably being only 650°C to 850°C amounts to;
• - Hot forming of the sheet steel material or the sheet steel blank to form a sheet metal part, for which purpose the press-hardening tool performs a continuous or uninterrupted closing movement;
• - Cutting the sheet metal part in the press-hardening tool to produce an outer contour before the closing movement reaches its bottom dead center;
• - finish forming the trimmed sheet metal part while the closing movement is continued to its bottom dead center and press-hardening of the sheet metal part in the bottom dead center of the closing movement;
• - Opening the press-hardening tool (by an opening movement) and removing the trimmed and press-hardened shaped sheet metal part, the average removal temperature preferably being below 200°C.

A closing movement is understood to mean, in particular, the downward movement of an upper tool part (upper tool) coupled with a downward stroke of the ram (of a press ram) to a bottom dead center. Under a continuous Closing movement is understood to mean that this closing movement is carried out without time interruptions up to bottom dead center, with the movement speed also being able to vary as a function of the path.

In the method according to the invention, the shaped sheet metal part is trimmed in the press-hardening tool before the shaped sheet metal part is finished, the shaped sheet metal part still having a preform (preform trimming). The sheet metal part that has not yet been completely formed can also be punched. Only after trimming is the shaped sheet metal part finish-formed and press-hardened at bottom dead center (BDC), in particular by applying a sufficiently high contact pressure (preferably at least 0.1 MPa/mm ² ) with cooled tool parts. A strength of at least 1300 MPa is preferably achieved here. The trimming takes place (in the same clamping or press stroke) before the press hardening, so that on the one hand the cutting forces and the mechanical loads on the cutting knives are comparatively low and on the other hand a more favorable cut surface formation (e.g. due to reduced edge crack sensitivity or crack tendency and low breakage) on the sheet metal part is reached.

During trimming, at least one cut surface that forms the outer contour is produced on the shaped sheet metal part using at least one cutting blade or the like arranged in the press-hardening tool. In particular, it is provided that a final trimming already takes place in the press-hardening tool, such that the outer contour no longer has to be trimmed after the press-hardened sheet metal part has been removed from the press-hardening tool, at least in the relevant areas. According to the invention, at least one cut surface (external cut surface) produced during trimming in the press-hardening tool is further retracted during the finish forming (until the final shape is reached). The arrangement of the cutting blade(s) in the press-hardening tool is preferably carried out taking this “further” indentation into account, which can be determined, for example, with the aid of forming simulation or surface (reverse) development.

During final forming, (at least) one cut surface (external cut surface) produced during trimming on the shaped sheet metal part can be moved or pulled via a cutting blade, in particular a lower cutting blade, of the press-hardening tool, with the burr being smoothed out on the relevant cut surface. Smoothing works particularly well because the sheet steel material is still warm (see below) or has not yet been press-hardened.

During the cutting of the shaped sheet metal part or the preform, the sheet steel material preferably still has a temperature of more than 400°C, in particular more than 450°C. The process can therefore also be referred to as hot trimming or hot trimming. The temperature is therefore above a martensite start temperature (Ms temperature) at which the martensitic transformation desired during press hardening begins, but at least significantly above a martensite finish temperature (Mf temperature) at which the martensitic transformation is complete. In particular, it is provided that the martensitic microstructural proportion is less than 10% by volume during trimming.

The sheet metal part or the preform is preferably trimmed between 12 mm and 1 mm, particularly preferably between 6 mm and 1 mm or between 6 mm and 2 mm and in particular between 4 mm and 1 mm or between 4 mm and 2 mm before the closing movement has reached its dead center (BDC), so that, depending on the sheet thickness (of the sheet steel material), there is still sufficient residual closing path or residual drawing path for finish forming of the trimmed sheet metal part. The remaining closing path is preferably at least 1.0 mm, in particular at least 2.0 mm.

According to the invention, during the hot forming of the sheet steel material to form a shaped sheet metal part, the sheet steel material or the shaped sheet metal part formed from it is fixed by means of at least one hold-down device belonging to the press-hardening tool in order to prevent slipping. This is a spring-loaded or spring-loaded hold-down device that presses the sheet steel material against the punch of the press-hardening tool. The press-hardening tool can also have a sheet metal holder, which presses the sheet steel material or the shaped sheet metal part formed from it in the edge area (flange) against the die of the press-hardening tool.

The sheet metal part is preferably trimmed using at least one lower cutting blade and at least one upper cutting blade. An unchangeable, i. H. fixed preset cutting gap between the lower cutting blade and the upper cutting blade can be in the range of 0.05 mm to 3.00 mm, preferably in the range of 0.05 mm to 1.00 mm, or can preferably be 0.20 mm, whereby a favorable cutting surface formation (see above) on the shaped sheet metal part and/or long knife service lives can be achieved. At least one of the cutting blades can preferably be cooled and is designed for this purpose, for example, with cooling bores (for a cooling liquid).

The cut waste can remain connected to the sheet metal part via narrow, in particular non-press-hardened, webs and can be separated from the sheet metal part after joint removal from the press-hardening tool. The cut waste can (after complete separation from the formed sheet metal part) also be removed from the press-hardening tool via chutes and/or shafts and, for example, collected in collection containers. Preferably, the offcut areas are not press hardened.

A press-hardening tool suitable for carrying out the method according to the invention is intended for use in a forming press (so-called press tool) and has a lower tool part to be arranged on the press table and an upper tool part to be fastened to the press ram. At least one cutting blade (or the like) is arranged in the lower part of the tool and/or in the upper part of the tool, with which a shaped sheet metal part to be produced (which is located between the lower part of the tool and the upper part of the tool) is cut during the hot forming (i.e. before the shaped sheet metal part is finished forming into the final shape) with a continuous closing movement of the Can be trimmed upper part of the tool or the ram downstroke before the closing movement of the upper part of the tool or the downward stroke of the ram has reached its / its bottom dead center at which the (final) press hardening takes place. Analogously to the previous explanations, the press-hardening tool is also designed so that (after the trimming) the trimmed sheet metal part can be finish-formed during the continued closing movement down to the bottom dead center. The press-hardening tool can also have at least one punch or the like for hot punching. Further developments and refinements of the press-hardening tool result analogously to the method according to the invention.

• - hohe Wirtschaftlichkeit;
• - einfacher Werkzeugaufbau möglich;
• - wenig Verschleiß des/der Schneidmesser aufgrund geringer Schneidmesserbeanspruchung;
• - geringe Schneidkraft;
• - günstige Schnittflächenausbildung, insbesondere geringe Rissneigung und kleiner Bruchanteil;
• - Energieersparnis (insbesondere im Vergleich zu einem Laserbeschnitt);
• - allenfalls geringe Gefügebeeinflussung beim Beschneiden.

The invention also has the following advantages (not an exhaustive list):

• - High profitability;
• - simple tool construction possible;
• - little wear of the cutting blade(s) due to low cutting blade stress;
• - low cutting force;
• - Favorable cut surface formation, in particular low crack tendency and small fraction;
• - Energy saving (especially compared to laser trimming);
• - At most, slight structural influence when trimming.

• 1 bis 3 veranschaulichen in schematischen Schnittdarstellungen einen erfindungsgemäßen Verfahrensablauf (in zeitlicher Abfolge) zur Herstellung eines pressgehärteten und beschnittenen Blechformteils.
• 4 zeigt ein Detail aus 3 (entsprechend dem in 3 gekennzeichneten Bereich A).

The invention is explained in more detail below by way of example with reference to the figures, without thereby restricting the scope of the invention.

• 1 until 3 illustrate in schematic sectional representations a process sequence according to the invention (in chronological order) for the production of a press-hardened and trimmed sheet metal part.
• 4 shows a detail 3 (according to the in 3 marked area A).

1 shows a tool area of a press-hardening tool 100, which has an upper tool part with a die 110 and a hold-down device 120 and a lower tool part with a stamp 130 and a sheet metal holder 140 that can be displaced downwards. At least some of these tool parts are designed with tool cooling devices (not shown). Lower cutting knives 150 (which can be designed both as separate cutting blades or cutting jaws and also as integrated cutting edges) are arranged on punch 130 . Upper cutting knives 160 (which can also be designed as separate cutting blades or cutting jaws as well as integrated cutting edges) are arranged on the die 110 and correspond to the lower cutting knives 150 . A single, in particular rotating, cutting blade 150 and/or 160 can also be provided in each case.

Between the upper part of the tool and the lower part of the tool there is a heated and austenitized sheet steel material M (e.g. a 22MnB5 or a 34MnB5 material, possibly also with an anti-corrosion coating), which is inserted into the press-hardening tool 100 as a sheet steel blank (possibly also as a tailored blank) and then through a continuous closing movement S or by a downward movement of the upper part of the tool (the closing or ram speed is, for example, 80 mm/s to 400 mm/s) is hot-formed and press-hardened to form a sheet metal part. According to the invention, the shaped sheet metal part is trimmed (possibly also punched) during hot forming, ie before the final shape is reached, and then finish-formed and press-hardened.

1 shows the start of hot forming. In this case, the sheet steel material M is fixed against the die 130 with the aid of the hold-down device 120 . 2 shows the advanced hot forming of the sheet steel material M just before the closing movement S of the tool upper part reaches its bottom dead center, e.g. between 4 mm and 2 mm before BDC.

With the aid of the cutting blades 150, 160, the outer contour is trimmed (hot trimmed) on the sheet metal part that has not yet been fully formed, which can also be referred to as preform trimming. The trimming takes place according to the closing movement S from top to bottom, preferably with a scissor cut (cross cutting) or wave cut. 2 shows the time of the incision. Due to the lack of contact pressure between the die 110 and the punch 130 and a comparatively low contact pressure between the die 110 and the sheet metal holder 140, the sheet metal component is not yet (martensitic) hardened at the cutting lines, at least not yet fully hardened.

During the further closing movement S up to bottom dead center UT (here the press-hardening tool 100 is completely closed), the trimmed sheet metal part is finish-formed into the intended final shape and then press-hardened at bottom dead center UT in a known manner by contact pressure with the cooled tool parts (a specific , in particular sheet thickness-dependent, be provided locking time, during which the tool upper part remains in the bottom dead center UT), as in 3 shown. During this final forming, the cut surfaces F produced during trimming on the shaped sheet metal part (possibly it is also only a single, in particular circumferential cut surface) are drawn in further, as in 3 and 4 illustrated by the arrows E, and thereby assume their intended end positions (corresponding to the final shape), so that at least there no trimming is required after the sheet metal part has been removed from the press-hardening tool 100 . As a result of this further indentation E, cutting burrs on the cut surfaces F of the shaped sheet metal part can be smoothed out on the lower cutter 150, as described above. Possibilities of disposing of cutting waste from the press-hardening tool 100 are explained above.

reference list

100

press hardening tool

110

die

120

hold-down

130

Rubber stamp

140

sheet metal holder

150

cutting knife

160

cutting knife

A

detail

E

further entry

f

cut surface

M

sheet steel material

P

cutting gap

S

closing movement

subtitles

bottom dead center

Claims (5)

Process for the production of a press-hardened and trimmed sheet metal part, with the steps: - Inserting a heated and austenitized sheet steel material (M) in a press hardening tool (100) having a die (110) and a punch (130); - Hot forming of the sheet steel material (M) into a shaped sheet metal part, for which the press-hardening tool (100) executes a continuous closing movement (S), with the sheet steel material (M) being hot-formed by means of a spring-mounted hold-down device (120) belonging to the press-hardening tool (100), which steel sheet material (M) pressed against the punch (130) is fixed to prevent slipping; - Trimming of the sheet metal part in the press-hardening tool (100) to produce an outer contour before the closing movement (S) reaches its bottom dead center (UT) and before the sheet metal part is finished forming, with the steel sheet material (M) still being fixed by means of the hold-down device (120). ; - Finish forming of the trimmed sheet metal part while the closing movement (S) is continued to its bottom dead center (BDC), with at least one outer cut surface (F) produced during trimming on the sheet metal part being further retracted during finish forming, and press hardening of the sheet metal part in the bottom dead center (BDC ) the closing movement (S); - Opening the press-hardening tool (100) and removing the press-hardened and trimmed sheet metal part. procedure after claim 1 , characterized in that an outer cut surface (F) produced during trimming on the shaped sheet metal part is drawn in further during final forming and is thereby moved over a cutting blade (150) of the press-hardening tool (100), the cutting burr on the outer cut surface (F) being smoothed out. Method according to one of the preceding claims, characterized in that the sheet steel material (M) still has a temperature of more than 400°C during cutting. Method according to one of the preceding claims, characterized in that the trimming of the shaped sheet metal part is between 12 mm and 1 mm before reaching bottom dead center (UT). Method according to one of the preceding claims, characterized in that the sheet metal part is trimmed using at least one lower cutting blade (150) and at least one upper cutting blade (160), the cutting gap (P) between the lower cutting blade (150) and the upper cutting blade (160 ) is in a range from 0.05 mm to 1.00 mm.

Images