An independent educational resource built around historical WJT Associates themes: practical plastics processing, molding troubleshooting, process discipline, tooling qualification, training, and production engineering. This site does not represent the former WJT Associates consulting business or Bill Tobin.
Start here
WJT Associates and Injection Molding Process Knowledge
Understand what the historical WJT Associates domain covered — process engineering, tooling qualification, troubleshooting, training, and project management — and why those themes still matter for buyers and processors.
Read the historical context guideCoverage
Published
A buyer- and processor-focused guide to the historical WJT Associates themes: injection molding process discipline, tooling qualification, troubleshooting, training, and production engineering.
A practical guide to evaluating injection molding training ROI, learning motivation, process discipline, setup sheets, scrap reduction, and shop-floor behavior.
A practical framework for diagnosing and eliminating flash in injection molding. Covers root cause logic, process window discipline, mold vs. machine separation, and why random setting changes make flash worse.
A practical guide to injection mold qualification, T1/T2/T3 sampling discipline, process window documentation, setup sheets, and what buyers and processors should expect before a mold is approved for production.
A practical guide to improving profitability in injection molding through quoting discipline, documented process windows, setup control, customer management, and better separation of technical and commercial problems.
A shop-floor method for troubleshooting injection molding defects by root cause instead of trial and error. Covers the five defect families, the change-one-variable rule, and a structured diagnosis sequence.
Intermittent short shots, micro voids, and inconsistent cushion are often a worn non-return valve, not a process problem. How to read the symptoms, run a check-ring test, and decide when to pull the screw.
Cooling is the longest part of most cycles and the most neglected. How undersized fittings, laminar flow, and blocked lines starve a mold — and how to confirm the tool is actually getting the water it needs.
A molding press earns nothing during a changeover. How to treat setup reduction as a cash decision, separate internal from external setup, and shrink the time between the last good part of one job and the first good part of the next.
Regrind makes acceptable parts more often than designers fear — and ruins them more quietly than molders admit. How heat history, degradation modes, ratio control, and lot traceability actually work on the floor.
Cp and CpK are tools, not trophies. How process capability really works on the molding floor, why a frozen CpK lies as tooling wears, and how to use capability data to improve profit instead of just generating charts.
Decoupled molding without the mystique: separating fill from pack, why velocity-controlled filling matters, the foundational studies that build a robust process, and how to keep the black box honest.
Most molding disputes come from never agreeing what a good part is. How to write dimensional, functional, and cosmetic acceptance standards that hold up — and why 'no visible defects' is a trap for everyone.
When you specify a part's finish you're really specifying the mold's. Why 'bright shiny high polish' starts fights, how the SPI and VDI finish standards work, and how to communicate finish so both sides mean the same thing.
Running the screw dry to swap colors looks cheaper than purging compound — until you count the scrap, the streaks, and the hours. How changeovers really work and when purge compound pays for itself.
Why running maximum clamp isn't the safe default, how the tons-per-square-inch rule of thumb really works, and how to size clamp tonnage from projected area and melt index without crushing vents or flashing parts.
Building replacement tooling isn't just a purchase order. Why a 'better' new mold can make parts that no longer fit, how worn tooling becomes the de facto standard, and how to retool for seamless drop-in production.
Setup is where tools get crushed and bad process gets baked in. How low-pressure mold protection works, what each plastic-side parameter actually controls, and the first-article discipline that keeps setup scrap out of production.
Wet resin splays, degrades, and loses strength — and the damage is often invisible. How desiccant drying works, why over-drying is as bad as under-drying, and the material-prep discipline that prevents the defects nobody traces back to the dryer.
A molding press runs thousands of hours a year, and neglected maintenance shows up as scrap and downtime. A tiered preventive-maintenance schedule — operator daily checks through annual teardown — and the wear signals that masquerade as process problems.
Send one drawing to five toolmakers and you get five different prices. A look inside how a mold quote is built line by line, how shops turn an estimate into a quoted price, payment-milestone conventions, and why the numbers diverge.
A molded part's price isn't resin plus a markup. A look at the molder's per-part cost build-up — machine time, fixed-cost allocation, tooling amortization, material and secondary ops — and the levers a shop actually controls.
Requisition 1,200 pounds to ship 1,000 and the missing 200 didn't vanish — it leaked through runners, purge, scrap, and fuzzy weight definitions. How to account for material and find the loss that turns a job into a money loser.
Every shop has a back corner where old molds rust — tools you hold, customers own, and you're liable for. How to inventory consignment tooling, clean house without legal risk, and keep the records that vanish exactly when you need them.
'Make it strong' and 'make it sealed' aren't specifications. How to define the real load and seal requirement, then choose among snap-fits, screws, welding, and bonding — permanent versus serviceable — without over-building or under-sealing.
Quality's real goal isn't catching defects — it's making more saleable parts per run, which means profit. The four costs of quality, why inspecting harder doesn't help, and how to find the point where more quality costs more than it saves.
A weld line is two melt fronts that met too cool to fully fuse — a cosmetic mark and a real weak spot. Why they form, the process, mold, and design causes, and how to control where they land instead of pretending they aren't there.
Sink and voids come from the same thing — thick sections shrinking as they cool — and which one you get depends on whether the skin holds or pulls in. The design, pack, and gate causes, and why thinning the wall beats chasing pressure.
Warp is differential shrink — when one part of a molding shrinks more than another, it bends. The cooling, wall-thickness, fiber-orientation, and ejection causes, plus why a flat part at the press can warp in the box.