Apparatus and method for piercing and trimming hot stamped parts

A die apparatus including a first die element and a second die element is provided. The first die element is arranged with the second die element for disposal of a blank therebetween and includes a coolant channel and a trim groove for alignment with a trim line of the blank. A groove insert is disposed within the trim groove arranged to support a portion of the blank extending thereover and to reduce a cooling rate of the blank. The groove insert may be of a material including reflective radiation characteristics to reduce heat transfer from portions of the blank adjacent the trim line. The first die element may include a cavity aligned with a pierce region of the blank so that the pierce region does not contact an adjacent die element surface.

TECHNICAL FIELD

This disclosure relates to an apparatus and method for piercing and trimming blanks to form vehicle components.

BACKGROUND

Modern vehicle body structures are increasingly utilizing hot stamping to form complex part geometries and to achieve ultra-high strength steel (DHSS) properties. Utilizing DHSS presents challenges for trimming and piercing operations relating to severe wear and sometimes unexpected failure in trimming and piercing tools. Trimming is an operation in which unwanted portions of a blank or vehicle component are cut off to achieve a final vehicle component shape. Piercing is a shearing operation used to create openings or holes in a blank or vehicle component.

Traditional die trimming operations for DHSS vehicle components may create micro-cracks and other quality problems in trimmed edges or pierced openings of the vehicle component. Issues with traditional die trimming operations led to a use of laser trimming. Prior art manufacturing processes use laser trimming after stamping and die quenching operations. The use of a laser trim apparatus requires higher capital investment and a larger space in comparison to traditional die trimming and piercing stations. For example, a laser trimming process may amount to 20% to 50% of a total cost to manufacture a hot stamped vehicle component.

This disclosure is related to solving the above problems and other problems summarized below.

SUMMARY

A die apparatus includes a first die element and a second die element. The first die element is arranged with the second die element for disposal of a blank therebetween and includes a coolant channel and a trim groove for alignment with a trim line of the blank. A groove insert is disposed within the trim groove arranged to support a portion of the blank extending thereover and to reduce a cooling rate of the blank. The groove insert may be of a material including reflective radiation characteristics to reduce heat transfer from portions of the blank adjacent the trim line. The first die element may include a cavity aligned with a pierce region of the blank so that the pierce region does not contact an adjacent die element surface. A first portion of the coolant channel may be spaced approximately six millimeters from a die element surface and a second portion of the coolant channel may be spaced more than six millimeters from the die element surface. The coolant channel may be shaped to conform to the trim groove and a surface of one of the first die element and the second die element. The coolant channel may be gun drilled and form a V shape. An apex of the V shape may be spaced more than six millimeters from a respective die surface. The trim groove may have a depth between approximately 0.5 millimeters and 4.0 millimeters relative to a surface of the first die element. The groove insert may comprise two components sized to partially fill a volume of the trim groove and spaced from one another such that a gap therebetween is aligned with the trim line. The groove insert may be a single component sized to substantially fill a volume of the trim groove. The blank may be arranged with the first die element and the second die element so that another trim line is located outside of the die elements to avoid die cooling to reduce a cooling rate of the blank to prevent martensitic transformation.

A method of forming vehicle components includes heating a blank to induce blank austenitization; positioning the blank between two die elements so a trim line portion of the blank aligns with a trim groove of one of the two die elements; forming a vehicle component from the blank; and cooling the blank via heat transfer to the two die elements. The trim line is arranged with the trim groove to minimize heat transfer between the two die elements and portions of the vehicle component adjacent the trim line to form soft strength zones. Portions of the vehicle component other than the trim line are arranged between the two die elements for cooling at a rate sufficient for martensitic transformation. The method may further include identifying a pierce region of the vehicle component; and aligning a cavity of one of the two die elements with a pierce region of the vehicle component to minimize heat transfer between the two die elements and the pierce region to form another soft strength zone at the pierce region. The method may further include applying a coating upon a surface of the cavity or trim groove. The coating may have high radiation reflectivity characteristics to further reduce heat transfer between the two die elements and the pierce region. The method may further include positioning a groove insert in the trim groove to support a portion of the blank extending thereover.

A die apparatus includes first and second die elements spaced from one another to receive a blank therebetween. At least one of the first and second die elements includes a trim groove for aligning with a trim line of the blank, a coolant channel spaced from the trim groove, and a die element surface. The trim groove has a depth equal to two times a thickness of the blank and a width equal to ten to fifteen times the thickness of the blank so that the first and second die element cool regions of the blank adjacent the trim line at a rate slower than a critical cooling rate to prevent martensitic transformation. At least one of the first and second die elements may further define a cavity for alignment with a pierce region of the blank so that the pierce region does not contact an adjacent surface of the first and second die elements. The trim groove may have a depth between approximately 0.5 millimeters and 4.0 millimeters relative to a surface of one of the first and second die elements and a width between approximately ten millimeters and thirty millimeters. The apparatus may further include one of a groove insert for disposal within the trim groove or a coating applied to or formed upon a surface of the trim groove. The groove insert and the coating may each be of a material having reflector characteristics to reduce thermal heat transfer between portions of the blank adjacent the trim line and one of the first and second die elements. The groove insert may be sized to substantially fill a volume of the trim groove. The groove insert may include first and second components spaced from one another so that a gap between the first and second components is aligned with the trim line of the blank.

DETAILED DESCRIPTION

FIG. 1is a diagrammatic view of an example of a stamping process, referred to as a stamping process10herein. The stamping process10may operate with a die apparatus having a trim groove and a coolant channel configuration to form soft strength zones of a vehicle component along a vehicle component trim line to manufacture high quality vehicle components without issues related to traditional die trimming operations. The die apparatus of the stamping process10further removes a need for a laser trimming apparatus to reduce costs and eliminates a separate trimming station by including trimming and piercing operations with a vehicle component forming station.

For example, a coil apparatus14includes material for a blank wound about a central axis. The material may be cut in cutter16to create a blank. The blank may be positioned within a furnace18for thermal treatment to austenitize the blank. A first transfer apparatus20may transfer the now austenitized blank to a die apparatus22. In prior art processes as described above, the blank is then stamped into a vehicle component and quenched within a die apparatus. The vehicle component is then transferred to a trimming and piercing apparatus to cut off unwanted portions of the vehicle component and to pierce holes. In contrast, the die apparatus22forms, trims, and pierces the blank to form a vehicle component.

FIG. 2is a perspective view, in cross-section, of a portion of the die apparatus22. A first die element24includes a form cavity26, a first trim groove28, and a coolant channel30. The form cavity26is sized and shaped to form a vehicle component from a blank with a second die element and according to a design requirement. For example, the second die element may include a separate form cavity for alignment with the form cavity26to form a vehicle component as further described herein. The first trim groove28is aligned with a trim line of the vehicle component to assist in forming a soft strength zone on either side of the trim line. In one example, the soft strength zone is targeted to have a tensile strength of no more than 1000 MPa at a trim region or a pierce region and a target of less than 1300 MPa at other portions of the vehicle component.

The coolant channel30is variably spaced from the vehicle component to assist in forming the varied strength zones along the vehicle component. For example, the coolant channel30may be spaced closer to a die surface to increase heat extraction from the vehicle component and may be spaced further away from the die surface to reduce heat extraction from the vehicle component. The increased heat extraction forms harder strength zones and the reduced heat extraction forms softer strength zones.

FIG. 3is detailed view, in cross-section, of a portion of the first die element24. A vehicle component34is shown formed upon the first die element24. A trim line38separates the vehicle component34from a scrap portion40of the vehicle component34. The scrap portion40is trimmed from the vehicle component34to create a final product of the vehicle component34. The first trim groove28is shown aligned with the trim line38to provide a gap between a portion of the vehicle component34and a surface of the first die element24. This gap reduces heat transfer, e.g. reduces a cooling rate, between a portion of the vehicle component34, such as the portions on either side of the trim line38, and the surface of the first die element24located adjacent the coolant channel30.

FIG. 4is a schematic diagram illustrating a portion of the die apparatus22. The die apparatus22includes the first die element24and a second die element50. The first die element24and the second die element50are arranged with one another for disposal of a blank54therebetween. A fixture55may hold the blank54between the first die element24and the second die element50. The second die element50includes a second trim groove58. The first die element24and the second die element50are arranged with one another so that the trim line38is aligned between the first trim groove28and the second trim groove58.

A geometry of the trim grooves influences the cooling rates along the trim line38to prevent martensitic transformation and to form soft strength zones. For example, each of the trim grooves may have a depth60substantially equal to 0.5 millimeters to 4.0 millimeters. The depth60may be one to two times a thickness of the blank54. Each of the trim grooves may have a width62substantially equal to ten to thirty millimeters. The width62may be equal to ten to fifteen times the thickness of the blank54. In one example, the blank54may have a thickness of 1.5 to 2 millimeters. In this example, the depth60of each of the trim grooves may have a length equal to approximately 3 to 4 millimeters and the width62of each of the trim grooves may have a length equal to approximately 15 to 30 millimeters. The depth60and the width62of the first trim groove28may be optimized to vary with a thickness of the blank54and to vary with desired microstructures of the blank54adjacent the first trim groove28and the second trim groove58.

FIG. 5Ais a perspective view showing another example of a trim groove and trim groove insert for the first die element24of the die apparatus22. In this example, the first die element24includes a trim groove70, a first cavity76, and a second cavity78each for alignment with a portion of a blank or vehicle component for trimming or piercing. It is also contemplated that the first die element24may only include the trim groove70or only include one of the first cavity76and the second cavity78. The trim groove70may be arranged upon the first die element24to extend along trim lines of a blank or vehicle component as described above.

Optionally, a groove insert80or a coating may assist with forming desired microstructures of portions of the blank or vehicle component for trimming or piercing operations. The groove insert80may assist in supporting a portion of the blank or vehicle component extending over the trim groove70. Each of the groove inserts84may be of a material to operate as a reflector to minimize heat extraction from adjacent coolant channels to further assist in forming desired microstructures in soft strength zones. In one example, each of the groove inserts84may be of a ceramic material having reflective radiation characteristics. The groove insert80may be sized and shaped to substantially fill a trim groove or may be shaped as strips for contacting a lower portion of the trim groove70and a portion of the blank or vehicle component extending over the trim groove70.

The coating may be of a material to operate as a reflector to minimize heat extraction from adjacent coolant channels (not shown inFIG. 5A). The coating may be applied to or formed upon a surface82of the trim groove70. The coating may be a low thermal heat reflective material or a radiation reflective paint to reflect heat back to the blank or vehicle component to maintain a cooling rate above a sub-critical cooling rate. The coating may be a powder coated material, electroplated, or a type of foil. It is contemplated that the first cavity76and the second cavity78may also include an insert or coating to assist in minimizing heat transfer from the portions of the blank or vehicle component located adjacent the first cavity76and the second cavity78.

FIG. 5Billustrates another example of a groove insert for the trim groove70, referred to as groove inserts84. The groove inserts84may comprise two components and fill a portion of a volume of the trim groove70. For example, each of the groove inserts84may be located on either side of a trim line of a blank or vehicle component so that a gap between the groove inserts84is aligned with the trim line. Each of the groove inserts84may be of a material to operate as a reflector to minimize heat extraction from adjacent coolant channels to further assist in forming desired microstructures in soft strength zones. In one example, each of the groove inserts84may be of a ceramic material having radiation characteristics.

FIGS. 6 and 7show further detail of the first cavity76and the second cavity78. The first cavity76and the second cavity78may be arranged upon the first die element24adjacent a location of the blank or vehicle component requiring a piercing operation, such as an opening for a fastener. The first cavity76and the second cavity78assist in forming microstructures having soft strength zone characteristics. For example, a first contact portion86may extend about a first non-contact portion88defined by the first cavity76. A second contact portion92may extend about a second non-contact portion94defined by the second cavity78. The non-contact portions may correspond to a portion of a blank or vehicle component requiring a piercing operation to provide similar benefits to those achieved with the trim grooves from a heat extraction perspective. For example, the portions of the blank or vehicle component extending over the first non-contact portion88and the second non-contact portion94are subjected to less heat extraction from an adjacent coolant channel in comparison to another portion of the blank or vehicle component in direct contact with a die element surface.

FIG. 8is a schematic diagram, in cross-section, of an example of a portion of a die apparatus for use with the stamping process described herein. The die apparatus includes a first die element102and a second die element104arranged with one another for disposal of a blank106therebetween. A fixture107may retain the blank106in a position so the blank106does not contact the first die element102and the second die element104after vehicle component formation. The first die element102and the second die element104may operate with one another to form the blank106into a vehicle component having variable microstructures and strength zones.

For example, the first die element102may include a first coolant channel110and a first trim groove112. The second die element104may include a second coolant channel116and a second trim groove118. Each of the first coolant channel110and the second coolant channel116form separate V shapes. Axis120intersects the blank106at a trim line121and intersects the coolant channels at an apex having maximum spacing from the blank106. A spacing between surfaces of the trim grooves and portions of the blank adjacent the trim line121reduces heat extraction by coolant flowing through the coolant channels in comparison to portions of the blank106closer to or in contact with die element surfaces. This reduced amount of heat extraction provides a lower cooling rate for the blank106to form soft strength zones having a microstructure of one or both of pearlite and ferrite. These soft strength zones of the blank106located adjacent the trim line121provide regions where trimming and piercing operations are less stressful on trimming and piercing tools in comparison to trimming and piercing operations of regions having a hard strength zone. It is contemplated that the first coolant channel110and the first trim groove112may be formed as an insert component for mounting within a cavity defined by the first die element102such that various insert components having various channel and groove sizes may be mounted to the first die element102.

Each of the first coolant channel110and the second coolant channel116are oriented at an angle126relative to a surface of one of the die elements. In one example, the coolant channels are oriented at an angle of between twenty and forty degrees relative to the respective surface of one of the die elements. The orientation of the coolant channels provides for a first length128between the coolant channels and a die element surface and a second length130between the coolant channels and a die element surface. The second length130is greater than the first length128so that a cooling rate of the blank106will be higher the closer the coolant channel is to the blank106.

The higher cooling rate will assist in forming microstructures of the blank106having higher strength zones in comparison to portions of the blank106subjected to a lower cooling rate. Each of the coolant channels may be gun-drilled. Use of gun-drilled coolant channels oriented at an angle relative to die element surfaces is also simpler than designing complex coolant channels variably spaced from or conforming to vehicle component shapes.

FIG. 9is a schematic diagram, in cross-section, of another example of a die apparatus for use with the stamping process described herein. The die apparatus includes a first die element140and a second die element142arranged with one another for disposal of a blank146therebetween. Each of the first die element140and the second die element142may include coolant channels (not shown inFIG. 9) spaced from respective die element surfaces located adjacent the blank146. A fixture147may hold the blank146between the first die element140and the second die element142.

In this example, the blank146is arranged with the die elements so that a portion of the blank146includes a trim line150located outside of a mouth152defined by the die elements. The portion of the blank146located outside of the mouth152will be air-cooled at a rate less than a cooling rate of portions of the blank146located closer to the coolant channels. Portions of the blank146located adjacent the trim line150will cool at a rate to reduce a cooling rate of the blank146to prevent martensitic transformation and to form microstructures of one or both of pearlite and ferrite and create soft strength zones adjacent the trim line150. The soft strength zones provide for less stress on trimming tools in comparison to trimming operations of hard strength zone portions.

FIG. 10is a flow chart illustrating an example of a method for forming multiple strength zones of a vehicle component using the stamping process described herein, referred to as a method200. In operation204, a blank is heated at a temperature to induce blank austenitization. The temperature output to induce austenitization is determined based on a material of the blank and on a thickness of the blank.

In operation206, a location for a trim line and/or a piercing region of a blank is identified.

In operation208, the blank is positioned within a die apparatus so that the trim line and/or pierce region is aligned with a trim groove and/or cavity of the die apparatus. Alternatively, the blank may be positioned within the die apparatus so that the trim line and/or pierce region are on a portion of the blank located outside of the die apparatus. The trim groove and the cavity may be similar to embodiments described herein.

In operation212, the die apparatus forms the blank into a vehicle component.

In operation214, the vehicle component is cooled to form predetermined microstructures via coolant flowing through the coolant channels or via the die apparatus. The coolant channels are variably spaced from the vehicle component to form predetermined microstructures of the vehicle component at, for example, the trim line and/or pierce region. The coolant channels may be spaced from the vehicle component to form soft strength zones having microstructures including one or both of pearlite and ferrite. Due to formation of the soft strength zones at the trim line and pierce region, traditional trim and pierce tools may be used instead of a laser trimming apparatus. Using these traditional trim and pierce tools provides for a reduced cycle time in comparison to use of a separate laser trimming apparatus and a reduced cost for the tools.

In operation216, the trim and/or pierce tool trims the vehicle component at the trim line and/or pierces the vehicle component at the pierce region.