Automotive steering column, located on steering wheel, is a device used by driver to control direction. It is device through which driver inserts car key when driving. Automotive steering column and steering wheel both belong to main and auxiliary instrument panel assemblies. Automotive steering column is generally composed of two or three plastic parts, with the most important being upper and lower protective covers.

 

Part Draft Angle Analysis vs. Texture and Steel Fit Condition
Drawing analysis revealed that front die end face only has a 3.5-degree angle, which may pose a risk of tearing. It is recommended to adjust it to 5 degrees or higher! Rear die angle is fine.

 

Part Thickness analyses
Product wall thickness remains relatively constant, with main wall thickness at 2.5mm.

 

Mould Injection Point

 

Mould Layout
It is recommended that upper and lower covers of steering column be made using same mold!

 

Slide&lifter direction analyses

 

Ejection system

 

Parts & Mould Analyses Report

 

Part draft angle analyses vs. texture and vs. steel fit condition
After draft testing and analysis, there were no issues with ejection angle in the front mold direction, and there were no issues with product's end ejection along slider direction!

 

Draft analysis shows that ejection angles of sliders on both sides are correct!

 

Part Thickness analyses

 

Product wall thickness remains relatively constant, with main wall thickness being 3.0 mm.
Mould Injection Point

 

Mould Layout
It is recommended that upper and lower covers of steering column be made using same mold!

 

 

Slide & Lifter Direction Analysis

 

Slope 1 structure requires an additional push block at the top of lifter!

 

Ejection system

 

This mold adopts a demolding mechanism of "push rod + lifter + straight ejector + nitrogen spring ejection and reset," and a side-pulling structure of "lifter + lifter rod" and "angled guide pillar + slider." Lifters and sliders are numerous and large, and surface of slider requires a textured finish, demanding high precision. Design points and summaries of above structures have been discussed previously and will not be repeated here.
For this mold, the most easily overlooked and most dangerous issue before design is problem of lifter sticking to mold. This mold was unsuccessful in the first trial molding process; plastic parts were difficult to remove during ejection, and plastic parts stuck to lifters. Plastic parts were manually pried out, making removal difficult. Upon return to factory, mold was carefully inspected. Draft angles of undercut area on inner side of plastic part were fine; problem was that draft angle within ejector pin was not properly adjusted, resulting in heavy EDM marks. After a second adjustment, ejection and removal of plastic part were successful after trial molding.
Based on structural characteristics, material characteristics, surface quality, and batch requirements of automotive steering column, a single-point open hot runner injection method was designed. This improved fluidity of molten plastic during injection molding, enhanced filling effect, saved solidified material in runner system after molding, increased molding cycle and production efficiency. Since mass production, this mold has proven effective due to its reasonable design and reliable operation, resulting in good economic benefits for customer and serving as a recent success story in production.
7 Conclusion
(1) Automotive steering column plastic parts require excellent appearance quality, high requirements for molding lines, and high requirements for mold manufacturing. Upper and lower steering columns are assembly parts and must not be misaligned after assembly, requiring small and uniform gaps. Due to multi-directional, multi-faceted, and recessed structure of plastic part, a moving mold slider core-pulling structure is used on outer side, and a lifter core-pulling structure is used on inner side.
(2) Molding parts have complex interlocking structures, and an integral fitting method is used to ensure machining accuracy. Moving mold slider needs to be clamped together with fixed mold to save on molding lines, thus ensuring appearance molding line requirements of plastic part.
(3) Ejection and reset mechanism uses a nitrogen spring ejection and reset method, which is stable and reliable, effectively ensuring balance of ejection and reset system, ensuring sufficient ejection distance for plastic part.
(4) A hot runner gating system is adopted to achieve a submerged gate, avoiding impact of gate marks on appearance quality of plastic part. Cooling water channels are designed in both fixed molding parts and movable lifter to ensure uniform and effective cooling of plastic part.