Spline products belong to slender special-shaped strip plastic parts, with complex cross-section shape, uneven wall thickness and long overall size. It is easy to produce various forming defects in the injection molding process, which directly affects product appearance and assembly precision. Combining with mould structure characteristics, raw material performance and field commissioning experience, we sort out the causes of common defects and practical improvement schemes to guide on-site stable production.
Product Bending and Warpage DeformationThe main reasons for product warpage are inconsistent cooling shrinkage speed caused by uneven wall thickness, unreasonable layout of mould cooling water channels leading to unbalanced local temperature, single feeding mode causing unbalanced material flow stress, and unbalanced ejection force pulling products to deform. In view of such problems, the layout of follow-up cooling water channels can be optimized, dense water channels are arranged at thick glue positions to realize synchronous cooling of the whole product, and the temperature difference between front and rear moulds is controlled within a reasonable range. Multi-point balanced feeding is adopted to balance melt flow direction, and strip balanced ejection structures are added to avoid local stress distortion. Finished products are placed flat after demoulding and cooled naturally with simple shaping tools to reduce artificial correction deformation, and raw material formula is properly adjusted to reduce forming shrinkage ratio.
Surface Shrinkage Depression Defect
Shrinkage marks mostly appear at product corners and thickened glue positions, mainly because the holding pressure cannot be effectively transmitted, the injection pressure and pressure maintaining time are insufficient, the flow channel design is small resulting in large pressure loss, and excessive mould temperature leads to continuous internal shrinkage after surface solidification. In the improvement process, local glue filling allowance can be reserved at easy shrinkage positions in the early stage of mould design, the flow channel and gate size can be appropriately enlarged to reduce material transmission pressure loss, and segmented pressure maintaining technology is used to extend the terminal pressure maintaining time to fully supplement shrinkage gaps. Properly reduce mould temperature to accelerate surface solidification, lower screw back pressure to control melt density, and optimize product structure to reduce local glue accumulation.
Parting Surface and Side Flash ProblemLong strip spline moulds have large-span parting surfaces, which are prone to poor fitting clearance. Insufficient clamping force, excessive injection pressure and speed, wear of guide positioning parts and oversized exhaust grooves will all cause flash overflow. It is necessary to re-grind and fit the full-length parting surface to ensure tight bonding, appropriately increase equipment clamping force, reduce injection pressure and filling speed, and replace worn guide parts in time. Standardize the depth of exhaust grooves to ensure only exhausting air without overflowing materials, and regularly clean sundries and oxide scales on the parting surface in daily production to keep tight mould closing state.
End Filling Shortage and Surface Bad LinesInsufficient melt flow power, low material temperature and unsmooth terminal exhaust will lead to incomplete filling of product ends. It can be improved by properly increasing barrel temperature, adopting fast feeding in the early stage and slow filling in the later stage, expanding cold material well structure and setting centralized exhaust positions at the terminal. Raw materials must be fully dried to eliminate internal moisture and avoid water lines and air lines on the surface. Stabilize injection speed to keep melt flowing smoothly, improve cavity polishing finish to reduce flow resistance, and appropriately increase mould temperature to enhance melt fusion effect and weaken obvious weld lines.
Demoulding Scratches and Unstable Size
Too small demoulding draft angle, rough cavity surface and excessive ejection speed will cause product surface scratches. The demoulding inclination can be reasonably increased, the inner cavity is finely polished, the ejection speed is slowed down, and the use of release agent is standardized to ensure uniform and thin spraying. The unstable product size is mostly caused by frequent parameter adjustment, fluctuating mould temperature and mixed use of different batches of raw materials. It is necessary to fix mature forming processes, stabilize mould temperature, unify raw material brands and specifications, and standardize ejection action to ensure consistent size of each batch of products.
SummaryMost forming defects of spline products are derived from unbalanced cooling, unbalanced material flow and difficult fitting of long-strip parting surfaces. The correct improvement idea is to optimize mould structure first, standardize raw material pretreatment secondly, and finely adjust forming process finally. Controlling uniform cooling effect and balanced feeding state in daily production can solve most appearance and size defects. Cooperating with regular mould maintenance work can effectively stabilize product quality and improve the qualified rate of long-term batch production.
