Injection Molding Machine Mold Opening Rack and Pinion Drive

Client Background#

An injection molding machine manufacturer builds large injection molding machines. The mold opening and closing mechanism of these machines is driven by a rack-and-pinion system, and for large machines this drive has to combine high precision with heavy load capacity. The customer came to us for a high-precision rack-and-pinion drive system for this mechanism.

Requirement & Challenge#

• Gear module M10 and rack module M10 — a large module, so the drive has to carry heavy load.
• Accuracy GB 6 grade with tooth surface hardened — this calls for grinding after heat treatment so that accuracy is held after hardening.
• Heavy-load conditions with frequent starts and stops — the mechanism opens and closes every cycle, so the drive sees repeated starting and stopping loads rather than steady running.

The main difficulty lies in the pairing. A gear and a rack are separate parts, but together they form one drive. If they are produced independently and by different routes, or if the rack is spliced from several segments, the meshing quality and the positioning accuracy of the opening and closing movement can suffer. Long racks in particular have to be made as multiple segments and joined.

Solution & Process#

1. Gears: hobbing followed by grinding, with accuracy held at GB 6 grade.
2. Racks: milling followed by grinding, with long racks produced as multiple segments and spliced.
3. Matching: gears and racks are supplied as matched pairs from the factory, so that meshing is verified before shipment instead of being left to assembly.

Result & Feedback#

• Mold opening and closing runs smoothly, and positioning accuracy meets requirements.
• Service life is 30% longer than with the original supplier.
• The drive system has been supplied for 200 injection molding machines.