Ignition switch is on/off switch of car's ignition system (usually using a key). It is main circuit that allows ignition coil to be turned on and off. Ignition switch consists of a lock cylinder, a lock housing, and electrical components. Lock cylinder is installed in lock housing, which is then mounted on the front dashboard of car.

Car ignition switch lock housing is shown in Figure 1(a), lock cylinder in Figure 1(b), its three-dimensional structure in Figures 1(c) and 1(d). Material is zinc alloy with a shrinkage rate of 0.6%.

Lock shell has four directions of holes and grooves: left, right, up and down. Holes and grooves in the left and right directions need to be pulled out by inclined guide pins. Holes and grooves in up and down directions are parallel to mold opening and closing directions. It is only necessary to install core on movable plate or fixed plate. Core pulling and resetting of holes and grooves in up and down directions can be achieved by using mold opening and closing movement.

 

(a) Lock shell

 

(b) Lock core

 

(c) Three-dimensional structure of lock shell

 

(d) Three-dimensional structure of lock core
Figure 1 Lock shell and lock core
Note: ① is C-direction hole and groove element; ② is D-direction hole and groove element; ③ is upper hole and groove element; ④ is lower hole and groove element.

(1) Analysis of C-direction hole ①, groove ① element and core pulling mechanism. There are 2 *3.2mm*7.0mm and 2*3.2mm*3.0mm mold holes in C direction, as well as 2.2mm * 18.6mm *11°, φ21.3mm*φ20.5mm*12.6mm, φ25.1mm*φ20.5mm*13.7mm, φ24.0mm*22.9mm, 2 *22.8mm*0.8mm*(5.2mm-2mm)/2*(7.8mm-2mm)/2, and φ25.1mm*18.6mm mold grooves. These mold holes and mold grooves are all on the left side of lock shell and perpendicular to lock shell axis. Cores for forming these mold holes and mold grooves can be installed on the left slide. Left inclined guide column of die casting mold is used to push left slide to drive left core to perform core pulling and reset movements during mold opening and closing.

(2) Analysis of elements of D-direction mold hole ②, mold groove ② and core pulling mechanism. In D direction, there are R11.8mm*19.9mm, φ20.5mm*8.4mm, φ21.3mm * 11.5mm, φ21.3mm*12.6mm mold holes and 2 * 22.8mm * 0.8mm * (5.2mm-2mm) / 2 * (7.8mm-2mm) /2, φ25.1mm*18.6mm mold grooves. These mold holes and mold grooves are all on the right side of lock shell and perpendicular to lock shell axis. Cores for forming these mold holes and mold grooves can be installed on the right slider. Right inclined guide column of die casting mold is used to push right slider to drive right core to perform core pulling and reset movements during mold opening and closing.
(3) Design of upper mold hole ③ element and core pulling mechanism. There is a φ15.2mm*(26.4mm-2.0mm) mold hole on the top. Axis of hole is parallel to die-casting mold opening and closing direction. Therefore, core for forming hole can be installed on fixed mold plate. Mold opening and closing movement of mold can be used to realize molding and core pulling of hole.
(4) Design of lower mold hole ④, mold groove ④ elements and core pulling mechanism. There is a 2*φ19.4mm*φ15.2mm*68° mold groove on the bottom. Axis of mold groove is parallel to die-casting mold opening and closing direction. Therefore, core for forming mold groove can be installed on movable mold plate. Mold opening and closing movement of mold can be used to realize molding and core pulling of mold groove. Since φ15.2mm*(26.4mm-2.0mm) mold hole and 2*φ19.4mm*φ15.2mm*68° mold groove overlap, core for forming φ15.2mm mold hole should avoid core for forming lower mold groove. Lock shell parting surface Ⅰ-Ⅰ is located below 1.0mm*1.0mm boss, as shown in E-direction view and B-B section view of Figure 1 (a). Due to presence of boss obstacle, φ18.0mm*4.5mm groove below boss needs to be pulled and formed using a core pulling mechanism.

Ignition switch lock core is installed in the hole of lock shell, as shown in the D-direction view of Figure 1 (b). Lock core parting surface Ⅱ-Ⅱ is set at joint surface of 2.0mm*φ18.0mm and φ19.1mm.
(1) Analysis of C-direction hole ①, groove ① elements and core pulling mechanism. In C direction, there are 3*1.3mm*8.0mm, 3*1.3mm*8mm*2.2mm*ϕ1.9mm, and 4.5mm*8.5mm mold holes and 1.2mm*ϕ5mm/2, 4.0mm*(ϕ19.1mm-ϕ15.3mm)/2 mold grooves. Since above mold holes and mold grooves are on the side of lock core, are perpendicular to axis of lock core, cores for forming these mold holes and mold grooves can adopt an inclined guide pin slider core pulling mechanism, inclined guide pin pushes slider to realize core pulling by opening and closing die casting mold.
(2) Analysis of elements of D-direction mold hole ②, mold groove ② and core pulling mechanism. In D direction, there are 3*1.3mm*8.0mm, 3*1.3mm*8mm*2.2mm*ϕ1.9mm holes, and 3.0mm*(ϕ19.1mm-ϕ15.3mm)/2 and 1.2mm*ϕ5mm/2 grooves. Above-mentioned holes and grooves are on the other side of lock core, are perpendicular to axis of lock core. Cores for forming these holes and grooves can be made with an inclined guide pin slider core pulling mechanism. Opening and closing of die casting mold is used to push slider with inclined guide pin to achieve core pulling.
(3) Analysis of elements and core pulling mechanism of hole ③ and groove ③ in E direction. In E direction, there are 12.1mm*20°*7.0mm*9.4mm*2.5mm*3.0mm*57° and 8.1mm * 3.3mm * 18.0mm holes. These mold holes are located above lock core, parallel to mold opening and closing direction. Core can be mounted on fixed mold plate, allowing lock core to be pulled and formed using opening and closing of fixed and movable molds.
Based on analysis of lock housing and lock core's shape and core-pulling structure, molds for forming lock housing and lock core are equipped with left and right core-pulling mechanisms, respectively. Interference is avoided during core-pulling.

 

Figure 2 Gating System and Ejector Design
1. Cold Slug Well Condensate 2. Lock Housing 3. Cold Slug Well Condensate 4. Diverter Cone 5. Ejector Rod 6. Lock Core 7. Cold Slug Well Condensate 8. Cooling Water Isolator 9. Backing Plate
Design of gating system and ejector rod is shown in Figure 2. Gating system consists of a main runner, diverter runners, gate, and cold slug well. Molten zinc alloy is injected through sprue bushing on fixed mold plate. After being diverted by diverter cone 4, melt flows from diverter channel through sprue into mold cavity, cold slug well of lock housing 2 and lock core 6.
After melt in mold cavity cools, push rod 5 pushes out molded lock housing 2, lock core 6, and solidified material in main channel, diverter channel, and cold slug well. Due to different shapes and qualities of lock housing 2 and lock core 6, to prevent material shortages and looseness in molded lock housing 2 and lock core 6, gate depth of molded lock housing and lock core should be same during mold manufacturing. If material shortages or looseness occur in any cavity during mold trials, gate depth of cavity with insufficient material can be deepened.

Molten zinc alloy transfers heat to mold through gating system (Figure 2: Design of gating system and ejector). As mold continues to operate, heat builds up. High mold temperatures can lead to reduced mechanical properties of mold components and overheating of molded lock housing and lock core. Main mold components experiencing high heat are sprue bushing, diverter cone, fixed mold insert, and movable mold insert. Cooling water circuits are required to reduce temperature of these components.

 

Figure 3 Cooling System Design
1. Plug 2. Water Pipe 3. O-ring 4. Cooling Water Joint 5. Fixed Platen 6. Moving Platen 7. O-ring 8. Cooling Water Joint 9. Gasket 10. Diverter 11. Moving Mold Insert 12. Fixed Mold Insert 13. O-ring 14. Sprue Bushing 15. Diverter Cone 16. Cooling Water Joint 17. O-ring 18. Cooling Water Joint 19. Plug 20. O-ring 21. Cooling Water Joint 22. Cooling Water Joint 23. Cooling Water Joint 24. Plug 25. O-ring 26. Cooling Water Joint 27. Cooling Water Joint 28. O-ring
(1) Design of cooling water channel of sprue sleeve. As shown in Figure 3D-D, a cooling water channel is opened in fixed mold plate 5 and sprue sleeve 14. Cooling water two-way joints 18 and 21 are installed at both ends of fixed mold plate 5, and a screw plug 19 is installed in sprue sleeve 14. An O-ring 20 is installed between fixed mold plate 5 and sprue sleeve 14 channel to prevent cooling water leakage. Cooling water enters from cooling water two-way joint 21, then flows through sprue sleeve 14 channel in two ways and merges before flowing out from cooling water two-way joint 18. Cooling water takes away heat, thus reduces temperature of sprue sleeve 14.
(2) Design of cooling water channel of diverter cone. As shown in Figure 3E-E, cooling water enters from cooling water two-way joint 8 of movable mold plate 6, flows through flow channel separated by diverter plate 10 in diverter cone 15, then flows out from cooling water two-way joint 16. In order to prevent cooling water from leaking out of gap between movable plate 6 and diverter cone 15, causing mold parts to rust, O-rings 7 and 17 should be installed on joint surface between movable plate 6 and diverter cone 15.
(3) Design of cooling water channel for fixed plate insert. In addition to cavity plate for forming lock shell and lock core, fixed plate 5 also has cores for forming various grooves and holes for lock shell and lock core. These molded parts are in direct contact with molten zinc alloy fluid, generating a large amount of heat, which requires cooling water, as shown in Figure 3A-A. Cooling water enters cooling water channel of fixed plate 5 and fixed mold insert from cooling water two-way joint 27, then flows out from cooling water two-way joint 26, taking away heat and playing a role in cooling. To prevent cooling water from leaking out, a screw plug 24 should be installed at terminal and bend of cooling water channel of fixed mold insert, O-rings 25 and 28 should be installed at joint between fixed plate 5 and fixed mold insert.
(4) Design of cooling water channel for movable plate insert. Because movable mold insert 11 contains a core that requires core pulling, its physical size is limited, requiring cooling system piping to be located within movable mold plate 6 below movable mold insert 11. Movable mold plate 6 also houses cavity plate for forming lock housing and lock core, as well as cores for various grooves and holes. As shown in Figure 3B-B, cooling water enters channels of movable mold plate 6 through two cooling water unions 22, exits through cooling water union 23, dissipating heat.

Based on structural analysis of lock housing and lock core, core pulling is required for both lock housing and lock core, respectively, in the left and right directions.

 

Figure 4 Core Pulling Mechanism Design
1. Left Front Wedge 2. Left Front Slider 3. Movable Mold Insert 4. Left Front Core 5. Main Channel Condensate 6. Right Front Core 7. Right Front Slider 8. Right Front Wedge 9. Left Rear Wedge 10. Left Rear Slider 11. Left Narrow Groove Core 12. Left Rectangular Groove Core 13. Right Rectangular Groove Core 14. Rear Center Core 15. Rear Center Insert 16. Right Narrow Groove Core 17. Right Rear Slider 18. Right Rear Wedge 19. Diverter Cone 20. Rear Right Insert 21. Rear Right Core 22. Right Front Core 23. Left Front Core 24. Rear Left Insert 25. Right Center Pressure Plate 26. Right Rear Core 27. Center Rear Insert 28. Right Front Core 29. Left front core 30. Center front insert 31. Rear left core 32. Left center pressure plate 33. Right end pressure plate 34. Left end pressure plate
(1) Core pulling mechanism on the left side of lock housing is shown in Figure 4. Left front slider 2 is installed in T-slot formed by left center pressure plate 32 and left end pressure plate 34. Left front slider 2 is equipped with left front core 4, 29 and inclined guide pin. When mold is opened and closed, inclined guide pin pushes left front slider 2 and left front core 4, 29 to perform core pulling and reset movements. When mold is closed, left front wedge block 1 can wedge left front slider 2 to prevent left front slider 2 and left front core 4, 29 from retreating under action of pressure and holding pressure, resulting in size of molded mold hole or groove not meeting requirements of drawing.
(2) Core pulling mechanism on the right side of lock housing is shown in Figure 4. Right front slider 7 and right front core 6, 28 can perform core pulling and reset movements under push of inclined guide pin. When closing mold, right front wedge block 8 can wedge right front slider 7.
(3) Core pulling mechanism above lock shell is shown in Figure 5. Front fixed model core 17 installed in fixed mold insert 16 can be pulled out of lock shell hole when mold is opened, and the front fixed model core 17 can be reset when mold is closed.
(4) Core pulling and demoulding mechanism below lock shell is shown in Figure 5. Front movable model core 19 is installed in hole of movable mold insert 21 in a clearance fit. When demoulding, push rod 22 pushes front movable model core 19 and lock shell 18 together. After demoulding, front movable model core 19 is manually removed from lock shell 18. Before mold is closed, front movable model core 19 needs to be manually placed in hole of movable mold insert 21.

Lock core also needs to be pulled in the left and right directions. A core needs to be set on the top, core pulling is completed by opening and closing movement.
(1) Core pulling mechanism on the left side of lock core is shown in Figure 4. Left rear slider 10 is installed in T-shaped groove composed of left middle pressure plate 32 and left end pressure plate 34. Left rear slider 10 is equipped with left narrow groove core 11, left rectangular groove core 12, three rear left cores 31 and inclined guide column. When mold is opened and closed, inclined guide column pushes left rear slider 10, left narrow groove core 11, left rectangular groove core 12 and three rear left cores 31 to perform core pulling and reset movements. When mold is closed, left rear wedge block 9 wedges left rear slider 10 to prevent left rear slider 10, left narrow groove core 11, left rectangular groove core 12, three rear left cores 31 from retreating under action of pressure and holding pressure.
(2) Core pulling mechanism on the right side of lock core is shown in Figure 4. Similarly, right rear slider 17 and right rectangular groove core 13, right narrow groove core 16 and right rear core 26, right rear slider 17 and right rectangular groove core 13, right narrow groove core 16 and right rear core 26 perform core pulling and reset movements under push of inclined guide column. When closing mold, right rear wedge block 18 can wedge right rear slider 17.
(3) Core pulling and forming of mold hole ③ above lock core is shown in Figure 5. Rear fixed mold core 29 is installed on fixed mold base plate 9. Mold opening and closing can realize core pulling and forming of mold hole ③ above lock core 30.

In addition to design of above-mentioned pouring system, cooling system and core pulling mechanism, lock shell and lock core die-casting mold structure design also includes design of mold frame, guide components, demoulding and reset mechanism, as well as selection and heat treatment of materials of main parts of mold. Only by fully dealing with these issues can mold structure be reasonably designed.

 

Figure 5 Die-Casting Mold Structure
1. Moving Mold Base Plate 2. Spacer Block 3. Ejector Plate 4. Ejector Rod Fixing Plate 5. Reset Rod 6. Moving Mold Plate 7. Guide Pin 8. Guide Sleeve 9. Fixed Mold Base Plate 10. Left Front Wedge Block 11. Left Front Slider 12. Screw 13. Inclined Guide Pin 14. Left Front Core 15. Pressure Plate 16. Fixed Mold Insert 17. Front Fixed Mold Core 18. Lock Housing 19. Front Moving Mold Core 20. Front right core 21. Moving mold insert 22. Push rod 23. Rear left wedge 24. Screw 25. Rear left slider 26. Inclined guide 27. Rear pressure plate 28. Left front rectangular groove core 29. Rear fixed mold core 30. Lock cylinder 31. Rear left core 32. Rear right core 33. Right front rectangular groove core 34. Left narrow groove core 35. Right narrow groove core 36. Rear center core push rod 37. Push rod 38. Push rod 39. Push rod 40. Push rod 41. Push rod 42. Backing plate 43. Cooling water isolation plate 44. Diverter cone 45. Sprue bushing 46. Rear left insert 47. Rear right insert 48. Side pressure plates 49. Two-Center Pressure Platen
Die-casting mold structure is shown in Figure 5. Mold frame consists of a movable die base plate 1, a spacer 2, a push plate 3, a push rod fixing plate 4, a reset rod 5, a movable die plate 6, guide pins 7, a guide sleeve 8, a fixed die base plate 9, a fixed die insert 16, a movable die insert 21, a diverter cone 44, a sprue bushing 45, push rods 22, 37, 38, 39, 40, and 41. Guide structure, consisting of four pairs of guide pins 7 and guide sleeves 8, ensures positioning and guidance of movable die plate 6 and fixed die plate 9 during mold opening and closing.

After lock case and lock core are formed, opening mold allows core to be pulled out of all grooves and holes in the lock case and lock core, eliminating obstacles to demolding lock case and lock core.
(1) Demolding of lock shell and lock core: As shown in Figure 5, demolding mechanism consists of a push plate 3, a push rod fixing plate 4, push rods 22, 37, 38, 39, 40, and 41. Under push of die-casting machine push rod, push plate 3 and push rods 22, 37, 38, 39, 40, and 41 on push rod fixing plate 4 can push lock shell 18 and lock core 30 out of cavity of movable mold insert 21.
(2) Resetting of demolding mechanism. As shown in Figure 5, reset mechanism consists of a push plate 3, a push rod fixing plate 4, and a reset rod 5. After demolding is completed, demolding mechanism must be immediately restored to the position before demolding in order to continue die-casting process. When fixed mold base plate 9 and movable mold plate 6 are molded together, fixed mold base plate 9 presses against reset rod 5 and pushes reset rod 5 to gradually retract until demolding mechanism is completely reset when fixed mold base plate 9 and movable mold plate 6 are molded together.

During die-casting process, surfaces of key components undergo internal stresses generated by erosion of molten metal and internal temperature gradients, compressive stresses due to differential expansion, and tensile stresses during cooling. These alternating stresses increase with number of die-casting cycles. When these stresses exceed fatigue limit of die-cast component material, plastic deformation and cracks at grain boundaries (thermal fatigue) can occur on the surface. Surface is susceptible to oxidation, hydrogenation, and gas corrosion, resulting in erosion wear and metal-to-metal adhesion or welding. Ignition switch lock cylinder is subject to mechanical loads during demolding. Key components are made of 4Cr5MoSiV1, heat-treated to 43-47 HRC, or 3Cr2W8V, heat-treated to 46-52 HRC. To prevent deformation, cracking, decarburization, oxidation, and corrosion of lock cylinder, heat treatment can be performed in a salt bath furnace, a protective atmosphere furnace, or in a vacuum furnace. Stress relief annealing should be performed before quenching to eliminate residual stresses from machining. Quenching should be performed using two preheating steps, followed by heating to specified temperature and holding, followed by oil or gas quenching. After quenching, main molded parts of die casting mold should be tempered two to three times. To prevent sticking, carbonitriding can be performed after quenching. After a certain number of die castings, main molded parts should be removed and carbonitrided again.
Two die castings of different shapes, made of same material and of similar quality, can be molded in two cavities within same mold. However, using same gating system for both die castings may result in underfill or looseness in mold cavity of higher-quality part. Gate depth of defective cavity can be adjusted through trial molds. After a certain number of parts have been molded in a die casting mold, fatigue cracks may form on mold surface of mold parts. In this case, parts in contact with melt flow should be removed and carbonitrided to ensure that main parts do not crack.