DITAI
Introduction
Thermoforming may look simple from the outside: heat a plastic sheet, form it over a mold, trim it, and deliver the finished part. In real OEM manufacturing, however, every stage affects the final product’s appearance, dimensional accuracy, assembly fit, surface finish, strength and packaging safety.
At DitaiPlastic, our thermoforming process is built around one goal: turning a customer’s drawing, sample or product idea into a stable, repeatable and export-ready plastic part. This requires more than one forming machine. It requires engineering review, material selection, mold strategy, sheet extrusion, forming control, CNC cutting, post-processing, surface finishing, assembly inspection and protective packaging.
This article explains our complete thermoforming process step by step, based on the 10-stage workflow shown above.
What Is Thermoforming?
Thermoforming is a plastic manufacturing process in which a thermoplastic sheet is heated until it becomes formable, then shaped over or into a mold by vacuum, pressure or mechanical assistance. After forming and cooling, the part is trimmed, finished, inspected and packaged.
Thermoforming is widely used for:
- Automotive plastic parts and covers
- EV and industrial equipment housings
- Medical plastic trays
- Electronics and ESD packaging trays
- Retail display parts
- Food-grade plastic trays
- Custom blister packaging
- Large-format plastic panels and shells
Compared with injection molding, thermoforming is often more suitable for large parts, lower-to-medium production volumes, faster tooling, larger surface areas and projects that require custom sheet materials, colors or textures.
Step 1: Consultation and Design
Every reliable thermoforming project starts before production. The first step is consultation and design review.
At this stage, we review the customer’s drawings, 3D files, samples, product photos or target dimensions. The goal is to understand not only the shape of the part, but also how it will be used.
Key questions include:
- What is the application of the part?
- Will the part be visible to the end user?
- Does the visible surface contact the mold during forming?
- Is the part transparent, colored, textured or painted?
- Does it need flame resistance, UV resistance, impact resistance or ESD protection?
- Will it be assembled with other plastic, metal or electronic components?
- Are there holes, clips, ribs, deep-drawn areas or tight tolerance points?
- What is the expected production quantity?
- How will the part be packed and shipped?
This early design review helps prevent common problems such as incorrect material selection, poor draft angle, uneven wall thickness, unstable trimming, difficult assembly or high finishing cost.
For custom OEM thermoforming, a drawing is not just a shape. It is the starting point for material, tooling, forming, cutting, finishing and quality planning.
Step 2: Mixed Color Masterbatch
For many thermoformed parts, color is not only an appearance choice. It can affect brand consistency, light transmission, outdoor durability, production repeatability and inspection standards.
Before plastic sheet extrusion, color masterbatch can be mixed with the base material to create the required sheet color. This is especially important when customers need:
- Brand-specific colors
- Consistent color across production batches
- Opaque plastic parts
- Colored packaging trays
- UV-resistant outdoor components
- Custom display parts
- Color-matched housings or covers
Color masterbatch must be mixed evenly. Uneven mixing may lead to visible streaks, color spots, batch-to-batch variation or inconsistent surface appearance after forming.
For projects that require precise color control, customers can provide Pantone numbers, color samples or existing product parts for reference.
Step 3: Extrusion Plastic Sheet
Thermoforming starts with the plastic sheet. The sheet material, thickness, color, texture and surface quality all influence the finished product.
Common thermoforming materials include:
- ABS
- HIPS
- PETG
- PC
- PP
- PVC
- ABS+ASA
- ASA
- HDPE
- Anti-static or conductive sheet materials
Different materials are used for different applications. For example, PETG, PC and PVC are often used for transparent display, clear covers or visible packaging. Flame-retardant ABS, PC or PVC can be used for electrical housings and equipment parts. ASA and ABS+ASA are suitable for outdoor applications because of their weather resistance. HDPE can be used where toughness, chemical resistance or impact resistance is required.
During sheet extrusion or sheet preparation, several factors must be controlled:
- Sheet thickness
- Color consistency
- Surface texture
- Material shrinkage
- Forming temperature range
- Impact strength
- Flame-retardant grade, if required
- UV or weather resistance, if required
- Anti-static or conductive performance, if required
Material selection is one of the most important decisions in the thermoforming process. If the material is wrong, later processes such as forming, trimming, painting or assembly cannot fully correct the problem.
Step 4: Mold Production
The mold determines the shape, surface quality and repeatability of the thermoformed part. Mold selection depends on the product’s material, quantity, appearance requirements and forming surface.
At DitaiPlastic, common mold options include solid aluminum molds, sand-cast aluminum molds, wooden molds and fiberglass molds.
Solid Aluminum Mold
A solid aluminum mold is machined from a full aluminum block. It is typically used for transparent products or parts where the visible surface directly contacts the mold.
Solid aluminum molds are preferred when the project requires:
- Transparent plastic parts
- Better surface finish
- Higher visible-surface quality
- More stable dimensional control
- Better polishing quality
- Mold-contact surfaces that must look clean and consistent
For clear products, mold surface quality is especially important because scratches, machining marks or surface defects can transfer visually to the formed part.
Sand-Cast Aluminum Mold
Sand-cast aluminum molds are commonly used for many standard production projects, especially non-transparent parts, colored parts and structural thermoformed parts.
They provide a practical balance between mold cost, durability and production stability. For many OEM thermoforming projects, sand-cast aluminum molds are suitable for batch production.
Wooden and Fiberglass Molds
Wooden molds and fiberglass molds are generally used only for very small quantities, early shape verification or projects where the customer wants to reduce initial tooling cost.
They are not suitable for mass production because they can deform more easily and cannot maintain the same dimensional or surface stability as aluminum molds.
Choosing the right mold is not only about mold cost. It is about product quality, production repeatability and long-term project risk.
Step 5: Vacuum Forming
Vacuum forming is the core forming stage. The plastic sheet is heated until it reaches the correct forming condition, then shaped over the mold by vacuum force.
The key is not simply “more vacuum.” The real control points are:
- Heating temperature
- Heating uniformity
- Sheet sag control
- Mold temperature
- Vacuum timing
- Forming speed
- Cooling time
- Draft angle
- Wall-thickness distribution
- Visible surface direction
If the sheet is not hot enough, the material may not stretch properly and fine details may not form. If the sheet is overheated, it may become too thin, deform, whiten or lose surface quality.
For transparent parts, surface cleanliness and mold quality are especially important. For deep-drawn parts, wall-thickness distribution must be evaluated. For assembly parts, the forming plan must also consider later CNC trimming and fixture positioning.
Vacuum forming may look like a short process, but it depends on many decisions made earlier: material, sheet thickness, mold design, mold surface, forming direction and product structure.
Step 6: CNC Cutting
After vacuum forming, the part still includes excess plastic around the edges. Holes, openings, trimming lines, slots and assembly features must be cut accurately.
CNC cutting is used to control the final part dimensions. Depending on part geometry, we may use 3-axis or 5-axis CNC cutting.
CNC cutting is critical for:
- Hole position
- Edge accuracy
- Assembly fit
- Openings and windows
- Slots and mounting points
- Repeatable trimming lines
- Multi-angle or curved structures
The most important point in CNC cutting is positioning. If the formed part moves during cutting, the hole positions and trimming lines will shift. For this reason, fixtures, vacuum holding, magnetic positioning or custom supports may be used to stabilize the part before machining.
CNC cutting is not just removing extra plastic. It is a precision step that affects whether the final part can be assembled and used correctly.
Step 7: Sand and Fill with Putty
After forming and trimming, some products require sanding, putty filling or surface preparation. This is common for large-format parts, painted parts, joined parts or products with high appearance requirements.
Sanding and putty work may be needed to:
- Smooth trimming marks
- Reduce visible seams
- Fill small surface defects
- Prepare bonding areas
- Improve paint appearance
- Create a more consistent surface
The process may include rough sanding, filling, medium sanding, fine sanding and dust removal. Each step affects the next one. If dust or uneven filler remains on the surface, spray painting may show particles, bubbles, poor adhesion or visible unevenness.
For high-appearance thermoformed products, surface preparation is often as important as forming itself.
Step 8: Spray Painting
Spray painting is used when the customer requires a specific color, surface finish or visual effect. It can also improve the final product’s perceived quality and consistency.
Painting may include:
- Surface cleaning
- Sanding
- Primer application
- Color matching
- Spray painting
- Drying or curing
- Surface inspection
Different finishes can be selected depending on the product requirement:
- Matte finish
- Glossy finish
- Textured paint
- PU coating
- Special visual effects
- Customer color matching
During painting, the process must control coating uniformity, film thickness, color consistency and adhesion. QC inspection checks for sagging, particles, color difference, missed spray areas and uneven surface.
For visible plastic housings, automotive display parts, equipment covers and retail display components, painting can be a key factor in final product quality.
Step 9: Assembly and Quality Control
Many thermoformed products are not delivered as single parts. They may need bonding, welding, screw assembly, brackets, inserts, labels, lights, screens, metal components or other accessories.
Assembly is also a quality-control stage. Before assembly, each part is checked for deformation, cracks, surface defects, trimming accuracy and dimensional deviation.
For multi-component products, matching numbers may be used for each set. For example, the housing, base, cover and accessories from the same set can be marked with the same number. This prevents parts from different sets being mixed, reducing the risk of uneven gaps, mismatched holes or poor assembly fit.
During assembly and QC, we check:
- Hole alignment
- Edge matching
- Gaps between parts
- Surface consistency
- Bonding strength
- Screw or fixture fit
- Painted surface quality
- Functional assembly
- Packaging readiness
The goal is not only to make individual parts. The goal is to deliver parts that can be assembled, installed and used smoothly.
Step 10: Packaging
Packaging is the final protection stage before shipment. A good thermoformed part can still be damaged if packaging is not designed correctly.
Packaging planning must consider:
- Product size and weight
- Surface finish protection
- Painted part protection
- Transparent part scratch prevention
- Stacking method
- Export shipping method
- Wooden case or carton requirements
- Labels and part identification
- Set-by-set packing, if required
For large-format thermoformed parts, packaging is especially important because surfaces may be easily scratched, deformed or damaged during transport.
Export-ready packaging helps protect product quality from the factory to the customer’s warehouse.
Why a Full-Process Thermoforming Supplier Matters
Thermoforming quality depends on the full process, not on one machine.
If design review, sheet selection, mold production, forming, CNC trimming, sanding, painting, assembly and packaging are managed separately, communication costs increase and quality problems become harder to trace.
A full-process supplier can evaluate the project as one system:
- Which material is suitable?
- Should the part use a solid aluminum mold or sand-cast aluminum mold?
- Which surface is the visible side?
- Will the part need painting?
- Can the part be formed in one piece?
- Does it need bonding or assembly?
- How should the formed part be held during CNC cutting?
- How should sets be numbered for assembly?
- How should the final product be packed?
This system-level thinking is especially important for custom OEM plastic thermoforming projects.
Common Thermoforming Applications
DitaiPlastic’s thermoforming process can be used for a wide range of custom plastic products, including:
- Automotive and EV plastic parts
- Medical plastic trays
- Electronics packaging trays
- ESD trays
- Industrial equipment housings
- Retail display components
- Food-grade plastic trays
- Custom blister packaging
- Large-format plastic shells
- OEM plastic covers and panels
Each application has different priorities. A transparent display cover may require a solid aluminum mold and careful surface protection. A flame-retardant equipment cover may require material-grade verification. A multi-component housing may require bonding, sanding, painting and set-by-set assembly control.
Thermoforming Process FAQ
What is the difference between thermoforming and vacuum forming?
Thermoforming is the broader process of heating and forming plastic sheet. Vacuum forming is one thermoforming method that uses vacuum force to pull the heated sheet onto or into a mold.
What materials can be used for thermoforming?
Common materials include ABS, HIPS, PETG, PC, PP, PVC, ABS+ASA, ASA, HDPE and anti-static or conductive sheet materials. The best material depends on transparency, strength, flame resistance, outdoor durability, impact resistance, ESD needs and forming depth.
Which mold is best for transparent thermoformed parts?
Solid aluminum molds are usually preferred for transparent products or visible surfaces that contact the mold because they provide better surface stability, machining accuracy and polishing quality.
Are wooden molds suitable for production?
Wooden molds and fiberglass molds are generally suitable only for very small quantities or early shape verification. They are not ideal for mass production because they can deform and cannot maintain the same stability as aluminum molds.
Why is CNC cutting needed after vacuum forming?
Vacuum forming creates the general shape, but CNC cutting controls final holes, openings, edges and assembly features. It is critical for dimensional accuracy and part fit.
Why do thermoformed parts need sanding and putty?
Sanding and putty help smooth trimming marks, seams, small defects and joined areas before painting or final finishing. This is important for high-appearance products.
Can thermoformed parts be painted?
Yes. Thermoformed plastic parts can be painted with matte, glossy, textured or special finishes. Surface preparation, primer, paint adhesion and QC inspection are important for painted parts.
Can DitaiPlastic assemble thermoformed parts?
Yes. Multi-component products can be bonded, screwed, fitted, inspected and packed as sets. Matching numbers can be used to prevent mixed parts and improve assembly consistency.
Conclusion
A finished thermoformed plastic part is the result of many controlled steps. Consultation and design define the direction. Color masterbatch and sheet extrusion control material and appearance. Mold production determines shape and surface quality. Vacuum forming creates the part geometry. CNC cutting controls final dimensions. Sanding, putty, painting, assembly and QC turn formed plastic into a usable product. Packaging protects the finished parts during shipment.
If you are developing a custom thermoformed plastic part, tray, housing, cover, display component or packaging product, send us your drawings, sample photos or dimensions. DitaiPlastic can help review the material, tooling, forming, CNC trimming, finishing and assembly plan before production.
Call to action:
Send your 3D file, drawing, PDF, sample photos or target dimensions for a free DFM review and quotation.
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