Two Processes, One Standard

Injection molding produces sliders, pulls and some end stops from engineering plastics. Stamping produces metal sliders, stops, pins and pulls from strip. The two processes share one requirement: the part must be made to a tool, using a recorded parameter set, with a measurement that proves it. An audit that only examines finished parts will miss the two dominant causes of field failure, which are tool wear and unrecorded parameter drift.

Walk both lines in the same visit if you can. The contrast is instructive: molding failures tend to be dimensional and gradual, while stamping failures tend to be geometric and sudden.

Machine and Tooling Condition

Ask for the machine list and the tool list, then compare both to the floor. For each machine in production, ask when the tool was last serviced and how many shots it has run since.

  • Tonnage, shot capacity and controller type for each molding machine.
  • Tool identification, cavity count, and the maintenance interval in shots.
  • Last tool service date and the work performed: polishing, insert replacement, gate rework.
  • Spare tool inventory, and whether a second tool exists for the highest-volume part.
  • For stamping: press tonnage, die identification, die height and last sharpening date.
  • Die storage: on a rack, oiled, labelled, and protected from knocks.

A factory with one tool for a high-volume slider has a single point of failure. That is a commercial risk as much as a quality one, and it belongs in the audit report.

Parameters Must Be Written and Locked

Ask for the parameter sheet for the part running on the machine, then compare it to the controller screen. This single comparison reveals more than an hour of interview.

  • Barrel temperature profile by zone, and the tolerance band around each setpoint.
  • Shot size, injection speed, hold pressure, hold time and cooling time.
  • Mold temperature and the actual measured mold surface temperature.
  • Clamp force and whether it is fixed or adjusted by the operator.
  • Who is authorized to change a parameter, and whether changes are logged.

Passing looks like a signed sheet, a locked controller with a password, and a change log with a name, a date and a reason. Failing looks like a handwritten note taped to the machine.

Material Control and Regrind

Regrind is the most common quiet cause of slider brittleness. Ask the question directly and watch whether the answer changes when the supervisor joins.

  • Resin grade and supplier lot for the running job, with the bag label visible.
  • Drying conditions for hygroscopic resins: temperature, time and dew point.
  • Regrind ratio, stated as a percentage, and where that ratio is enforced.
  • Whether regrind is segregated by colour and grade, or mixed in a single bin.
  • How contaminated or degraded material is identified and removed.
  • Whether the factory can prove the ratio from records rather than from memory.

A stated maximum of fifteen percent regrind with no weighing record is a claim, not a control. Ask to see the scale.

Stamping: Strip, Clearance and Burr

Stamping quality is largely decided by die clearance and strip condition. Ask for the strip specification, then ask how clearance is verified after a die repair.

  • Strip material, thickness and temper, with the mill certificate on file.
  • Die clearance stated in absolute units, not as a percentage only.
  • Burr height limit and the measurement method used to enforce it.
  • Whether parts are tumbled or deburred, and whether that process is validated.
  • Die sharpening frequency, recorded in strokes rather than in weeks.
  • Scrap segregation: whether offcut material can re-enter the process.

What to Measure, and How Often

Ask for the inspection plan, then ask to watch one inspection cycle performed without preparation.

  • Critical dimensions: slider length, width, channel opening, and pin position.
  • Functional force: pull-off and holding force measured on a calibrated gauge.
  • Gate remnant height, flash and short shots.
  • Colour against an approved standard under a defined light source.
  • Sample size and frequency per shift, written into the control plan.
  • Reaction plan when a result is out of limit: quarantine, adjustment, re-verification.

A passing inspection cycle takes a defined time, uses a named instrument, and produces a value written into a record for the current lot. An inspection that produces only a tick mark is not a measurement.

Maintenance, Spares and Uptime

Ask for unplanned downtime for the last three months by machine. Then ask what the top three causes were. A factory that tracks downtime can plan capacity; a factory that does not will always be surprised.

  • Preventive maintenance schedule with completed records.
  • Critical spares held on site: heater bands, thermocouples, ejector pins, die springs.
  • Whether maintenance staff are on shift or on call.
  • Mean time to repair for the most common failure.

Questions for the Line Leader

  • How do you know this tool is still producing within tolerance after ten thousand shots?
  • What do you do with the first twenty parts after a tool change?
  • Which parameter drifts most often, and how do you notice?
  • Show me a part you rejected today and tell me why.

The Actionable Audit Checklist

  • Machine and tool lists match the floor, with status for each item.
  • Parameter sheet on the machine matches the controller within the stated tolerance.
  • Parameter changes are logged with name, date and reason.
  • Tool service is recorded in shots, not only in calendar time.
  • Resin bags are labelled with grade, supplier lot and receipt date.
  • Drying conditions are recorded for hygroscopic materials.
  • Regrind ratio is enforced by weighing, not by instruction.
  • Burr height is measured with a stated method and limit.
  • Die sharpening is recorded in strokes.
  • First-off and last-off parts are retained and identified.
  • Functional force is measured per lot on a calibrated gauge.
  • Downtime data exists by machine and by cause.

What a Passing Answer Looks Like

Passing sounds like this: "Tool four-two was pulled at ninety thousand shots, we replaced the core insert, ran first-off inspection on twelve dimensions, and the pull-off force came back at the middle of the band." That answer links tool state, inspection and a functional result. It is the kind of answer YCC expects from any molding or stamping line it evaluates.