DITAIQuality in thermoforming is not a final inspection — it is a chain of measurements taken at every stage, because a defect introduced at sheet extrusion cannot be corrected after trimming. This page documents what we measure at each of the five production stages, the instrument we measure it with, and how often we take the reading.
- STAGE 01Extrusion plastic sheets1–12 mm thick, up to 2000 mm wide, any Pantone colour
- STAGE 02CNC aluminium mouldsCast, block, texture acid-etched and sliding-block tooling
- STAGE 03Vacuum formingZone-by-zone heating recipes recorded per machine, per part
- STAGE 04CNC plastic trimming28 machines, 16 of them five-axis
- STAGE 05Post-processingAssembly, painting, polishing and finishing
Before a production tool is cut, most programs start with prototyping — the cheapest place to find a problem is on the first sample, not on the first batch.
Every Control on One Page
Each row below is expanded in its own section, with the instrument and the shop-floor photograph that goes with it.
| Stage | What we measure | Instrument / method | Frequency |
|---|---|---|---|
| Sheet extrusion | Thickness and width | Roll-gap check, calipers on the same plane | At start-up, then every 20 m of sheet |
| Sheet extrusion | Colour | Colorimeter against the Pantone card | Every 20 m; retained sample per batch |
| Sheet extrusion | Functional properties | Vertical/horizontal combustion tester (GB/T 2408, UL); pendulum impact tester | Per material specification |
| Tooling | Mould dimensions | Formed-sample measurement, 3D scan, machined check fixtures | Every new mould, before release |
| Tooling | Surface and venting | Polishing plus evenly spaced vacuum-hole drilling | Every new mould |
| Vacuum forming | Heating temperature | Recorded zone-by-zone temperature recipe per machine and part | Every production run |
| Vacuum forming | Formed wall thickness | Ultrasonic thickness gauge | Multiple points on the formed part |
| Vacuum forming | Shape stability | Cooling fixtures on the four edges; vertical on-edge stacking | PP/PE and other shrink-sensitive parts |
| CNC trimming | Cut accuracy | Matched fibreglass or wooden holding mould with vacuum ports and embedded magnets | Every trimmed part |
| Painting | Colour, film thickness, uniformity | Spectrophotometer, thickness gauge, cross-hatch adhesion test, gloss meter | Test panel before the run, then in-process |
| Assembly | Fit, bond strength, function | Component inspection, tolerance check, stress test, functional test | Every assembled unit, plus final inspection |
Sheet Extrusion
Extrusion is the process of heating and melting plastic particles, then squeezing them through the roll mould into sheets of different thickness and surface appearance. Sheet thickness can be 1–12 mm, width can reach 2000 mm, colour can be any Pantone colour, and we can integrate different functions into the material. Because we run our own sheet extrusion lines, quality control starts before the material ever reaches a mould.
Thickness and Width
Thickness and width are set by the distance between the three roll moulds. At the beginning of production we measure the accuracy between the roll moulds so the gap matches the required sheet thickness.
After each 20 metres of sheet length we use calipers to measure the same plane of the sheet, which catches the uneven condition that occurs when material stacks up. At the same 20 metre interval we re-measure the distance between all of the roll moulds. Width is checked the same way.
Colour
The most important instrument for colour is the colorimeter. We can produce every colour on the Pantone colour cards, and while the sheet is being produced we use the colorimeter reading against the Pantone card to confirm the colour is within the error range. The harder question is how the colour stays consistent from batch to batch — colour can drift between batches, or even between the front and back sections of the same batch. Three controls hold it:
Control 01
Mixed in-house, not bought in
DitaiPlastic runs two large extrusion lines, and our sheet-making manager has over 20 years of experience. All sheet colours are mixed by us, and we confirm the colour powder and the raw-material particles are mixed thoroughly before extrusion.
Control 02
Colorimeter every 20 metres
To keep colour consistent across different parts of the same batch, we compare with a colorimeter every 20 metres of extruded sheet — so a drift between the front and back of one batch is caught while the line is still running.
Control 03
Recipe and retained sample
Each batch recipe — the ratio of colour powder to raw material, the mixing time and the heating temperature — is recorded in the computer under the customer name and production date. We also cut and keep a sample of every batch. When you reorder, the colorimeter compares the two batches during production so the colour error stays inside the range.
Functional Properties
We customise material by melting in different characteristic particles — fire-resistant, high-impact, cold-resistant, anti-corrosion and others. Each property is verified by test, not by specification sheet alone.
To test fire resistance we cut part of the sheet into a vertical/horizontal combustion test machine, which determines the non-combustibility of plastics under direct burning from a prescribed fire source. The test method follows the GB/T 2408 standard together with UL and other standards to determine the flame-resistance level; we will also test directly with a lighter to see whether it lights.
High impact is tested on a professional impact test machine, with the pendulum weight set per test in kilograms — or impacted directly with a digger. Other characteristics are tested on the appropriate machine in the same way. See our material range and test reports and certifications.
Aluminium Moulds
To make a perfect plastic product, one of the necessary conditions is a perfect mould. We build ours on our own CNC mould machines, which lets us control quality, price and delivery date together — and we remake a mould free of charge if it is damaged.
Choosing the Mould Type
Type 01
Cast aluminium
Usually used for solid-colour and textured-surface material. Cast aluminium is cheaper, and for products with a solid colour or textured surface it achieves the same effect as a block aluminium mould.
Type 02
Block aluminium
Often used for transparent products and for products with a height of less than 100 mm, where surface definition matters most.
Type 03
Texture acid-etched
Vacuum forming turns a flat sheet into a 3D product, so the sheet must stretch. When the texture sits on the sheet surface it stretches with it; on an acid-etched mould the texture is on the mould surface instead, so texture distribution stays very uniform after forming. Available in international standard colour codes — we can provide all codes.
Type 04
Sliding block
Applied to products with an under-cut structure. The sliding of the module gives better control over both moulding and demoulding of the product.
Once we receive your 3D files or your samples, our engineer analyses the design to check whether it suits the vacuum forming process and gives professional suggestions based on our experience. After all details of the drawing are confirmed, the engineer converts the drawings into mould drawings according to the shrinkage rate of the chosen material — which also means the material must be selected before the mould is made. After CNC machining is finished, we polish the mould and drill the vacuum holes.
Four Ways We Verify a Mould
Manufacturing the mould begins by adjusting the shrinkage rate on the 3D drawing. Verifying its dimensions afterwards uses four methods:
Method 01
Form and measure a sample
Use the finished mould to make samples on the vacuum forming machine, then verify the accuracy of the mould by measuring the sample dimensions.
Method 02
3D scan and compare
After the mould is completed it is scanned to obtain a new 3D drawing of the finished mould, which is then compared against the original drawing after shrinkage adjustment. The cost of this method can be very high, so it is used where it is justified.
Method 03
Machined check fixtures
For the more important parts of the 3D drawing we CNC-carve a fixture to the size of those features and offer it up to the finished mould to see whether it matches. For a TV display back cover, for instance, the areas that are glued and screwed are the critical ones, so those are the places we make fixtures for.
Method 04
Surface and venting
We control the surface quality of the mould by polishing and by drilling the vacuum holes. Neatly arranged drilling holes matter especially on texture acid-etched moulds, where an uneven vent pattern shows in the finished texture.
Vacuum Forming
Vacuum forming is one of the most common plastic processing processes: it turns a flat sheet into a 3D shape. It needs two inputs — the extruded sheet made from hot-melted raw-material particles, and the mould. The mould is installed into the vacuum forming machine and raised so it attaches to the melting sheet completely; the product is then cooled and released from the mould. Control of temperature is crucial throughout, and quality control at this stage breaks down into three parts.
Forming Temperature
Data, not memory
There are two heating plates inside the vacuum forming machine, and each heating plate is divided into many heating zones. Different materials, different material thicknesses and different product shapes stretch differently, so the temperature has to be precise for each individual zone. For each machine and each product we record the heating zone and its temperature — which is what makes the forming result nearly identical across different production batches. We do not rely solely on human experience; we rely on the recorded data.
Formed Wall Thickness
Vacuum forming is essentially a stretch-and-cool moulding process, so the material inevitably thins as it stretches. Calipers cannot reach most of the formed geometry, so we use an ultrasonic thickness gauge to measure the wall thickness at each area of the part — which shows where the material has become too thin to perform, and lets us adjust the forming temperature in time.
We also increase the area and thickness of the blank material while keeping the product quality: for the same product, a thicker sheet or a larger sheet area can change the result after forming considerably.
Shape Stability
Temperature is not the only thing that affects shape — what happens after forming matters just as much. Products made of PP or PE usually take longer to cool, and once moved away from the vacuum forming machine (whose cooling system sits above the heating area) they shrink easily and excessively. For those parts we make a fixture that holds the four edges of the product after forming to secure the shape. When forming is completed we also stack the products vertically, on their side, so a part that has not fully cooled is not deformed by its own weight — these materials are very sensitive to temperature.
CNC Trimming
CNC (Computer Numerical Control) is the further processing of the product after forming: removing excess material from the outside of the product to obtain the required size and shape, plus drilling and levelling. We have two types of CNC cutting machine — five-axis and three-axis — 28 in total, of which 16 are five-axis. Five-axis machines process 360 degrees in all directions, are fast and accurate, and suit complex structures, angles and curved surfaces. This makes us one of the largest CNC production departments in China. Our CNC engineers type in the program and the machine cuts the shape of the product automatically.
Holding the Part So the Cut Is Accurate
Accuracy at this stage is a work-holding problem. Take the five-axis machines as an example: before cutting, we make a fibreglass or wooden mould whose surface shape fits the shape of the product. We drill holes through this mould and embed magnets on one side of its surface.
During cutting, the vacuum pump extracts the air between the mould and the product through the air holes on top of the mould, while a second magnet is placed on the surface of the product. Between the magnet attraction and the vacuum suction, the product is firmly attached to the mould — which is what keeps the cut dimensionally accurate.
Post-Processing
In vacuum-formed products the early stages — sheet extrusion, mould making, forming and CNC cutting — are predominantly automated. It is the manual post-processing that truly elevates the quality of the final output. Our skilled workforce handles edge-scraping and deburring, gluing, assembly, velvet flocking, sanding, spray painting, polishing, laser engraving and silk-screening. These steps make sure the product not only meets precise specifications but also reaches a high level of aesthetic and functional quality, ready for final use or assembly.
Spray Painting
Quality control in spray painting is critical to a flawless finish and long-lasting durability. Each product is thoroughly cleaned, sanded and primed before spray painting begins, so the surface gives proper adhesion, smoothness and consistency. During and after painting we check colour accuracy, coating thickness and surface uniformity, and any imperfection — bubbles, streaks, uneven coverage — is addressed immediately.
Paint 01
Colour accuracy
Visual comparison against approved colour samples, with a spectrophotometer checking for precise colour matching. Test panels are painted before full production to confirm accuracy.
Paint 02
Coating thickness
Coating thickness and adhesion are separate checks. A suitable thickness gauge measures the coating against the specified thickness; a cross-hatch test assesses adhesion. The method must suit the coating and plastic substrate.
Paint 03
Surface uniformity
Visual inspection and touch tests identify imperfections, while a gloss meter confirms a consistent finish across gloss and matte surfaces.
Assembly
Quality control in assembly makes sure all components are properly aligned, securely bonded and functioning as intended. We inspect individual parts, verify precise fits, and test the strength and functionality of the assembled product, so the finished item meets its durability and performance standard before it moves to the next production step or to delivery.
Assembly 01
Component inspection
Each part is checked for defects such as warping, cracks or surface imperfections before assembly, so only high-quality pieces are used.
Assembly 02
Fit and alignment
Parts are assembled with precise alignment to ensure proper fit. Misalignments or gaps are identified and corrected during assembly, and tolerances are checked so all components fit seamlessly.
Assembly 03
Bonding and fastening
Whether the joint uses gluing, welding or mechanical fasteners, its strength and stability are tested. Visual inspection and physical stress tests verify that parts are securely bonded or fastened.
Assembly 04
Functionality testing
Assembled products are tested to confirm they function as intended — especially where there are moving parts or components that require a certain level of precision in operation.
Assembly 05
Final inspection
After assembly, a thorough final inspection verifies that the product meets all specifications — appearance, stability and performance — before it is packaged or sent for further post-processing.
Factory Tour
Step inside our 20,000 m² facility — from sheet extrusion to 5-axis trim, finishing and QC.
