What is thermoforming?
Thermoforming is a process in which thermoforming plastic sheet is heated between 100° Celsius to 200° Celsius, and vacuum or pressure is applied to form a specific shape. The word ‘Thermoforming’ is a combination of ‘Thermo’ which means ‘heat’ and ‘forming’ which means providing a shape.
Mainly two types of thermoforming processes are widely used in the industry, vacuum thermoforming and pressure thermoforming. In addition, the thermoforming process is classified as single sheet forming and twin sheet thermoforming.
In mechanical thermoforming process, there are two kinds of molds used, namely male and female mold to produce a usable product. The plastic sheet is heated and placed between the male and female mold. Male mold is moveable and it is given the shape of the product to be produced while a female mold is rigid in nature.
Few e.g., of thermoplastics used, are co-extrusion, laminate, mono-material, and the most common plastic is PET (Polyethylene Terephthalate). The thermoforming process has significant application in most of the leading industries such as automotive, aerospace, building & business equipment, construction material, medical products, food containers and food packaging etc.
Following thermoforming animation helps to understand how thermoforming components are manufactured.
What are thermoforming methods?
Thermoforming methods are divided into 2 parts respectively.
Vacuum thermoforming:
In vacuum thermoforming, thermoplastic is heated under a certain flow of temperature
and compressed against 3-D mold with releasing the air stuck between the sheet and the
mold. This thermoforming is cost-effective, tools can be used quickly in this and it
permits the production of large parts.
Pressure Thermoforming:
It is a plastic thermoforming manufacturing technique . Pressure thermoforming can
produce high definition plastic component parts. This forming utilize positive pressure to
form the plastic into mold.
Thermoforming Process:
Following key steps are part of the thermoforming process.
- Loading plastic sheet
- Clamping plastic sheet
- Heating plastic sheet
- Forming (Vacuum / pressure)
- Cooling thermoformed component
- Unloading parts
- Trimming
- Paint (optional)
- Assembly (optional)
- Packaging
Thermoforming Process Qualification & Specification:
The following table specified how different parameters are reviewed to finalize the thermoforming process parameters.
Do you want to download this form and fill details? That’s absolutely fine, you can click on the following link to download this thermoforming qualification and specification file.
Post Thermoforming processes:
The following processes are essential to form a final shape of parts and meet part specifications (color, fit-functions and dimensions)
C.N.C / Robotic Trimming:
Once the thermoforming process is over next process is to trim off excess materials and cut the cavity, holes on thermoformed components. Multi-axis C.N.C (computer numerical control) / robotic trimmer machine used to trim off excess plastic materials. C.N.C trimming machine gives a final shape, tolerance to the part.
Trimmer gives the final shape to a component based on a pre-programmed command. With a multidirectional axis, trimming operation is performed on complex shapes. Watch the following GIF.
Painting Process on Thermoformed plastic parts:
Automotive components like front and rear bumpers require painting. Paint gloss, adhesion, paint type, and quality is defined as per car manufacturer.
Assembly of thermoformed parts:
This process is optional and mainly depends on customer requirements. Few components require an assembly with other child parts. Eg. Front and rear bumper require additional hardware/fasteners assembly so they can be used directly on the assembly line
Is thermoforming tooling cost cheaper than injection molding tooling cost?
Yes. In thermoforming only one side of the plastic sheet is exposed to tooling whereas in injection molding male and female mold requires higher precision and also it requires high clamping force.
What is thermoforming plastic parts used for?
Thermoforming products used in various industries, refer to the following list,
Automotive Industry
- Front and rear bumper
- Dashboard
- Interior panels
Aerospace Industry
- Window Shades
- Flight interior parts
- Seat parts
- Compartment panels (panels for separation business class and economy class)
How to evaluate thermoforming process?
Following the 5M-1E methodology helps to evaluate the thermoforming process in your organization or at your supplier.
| Process Parameters | Questions |
| Material Storage | 1. How thermoforming sheets are stored in the warehouse? All sheets are stored on the pallet with covering its full length and width? 2. How FIFO is maintained in the warehouse? 3. How thermoforming sheets are identified in the warehouse with respect to batch/lot number, material grade, and type? 4. What precautions measure implemented in the warehouse to avoid thermoforming sheet mix-up? |
| Material Inspection & Testing | 1. Incoming inspection is being conducted for thermoforming sheets? 2. Lot number or batch number of thermoforming sheets is traceable to GRN (Goods Receipt Note / Number)? 3. Test certificates are collected from thermoforming sheet manufacturers? 4. Test certificate is traceable to raw material lot number/batch number? 5. Test certificate is traceable to purchase order and invoice? 6. Incoming inspection covers thermoforming material type, color, texture, dimension (length, width, and thickness), and grade? |
| Thermoforming sheet pre-heat and conditioning | 1. Pre-heat oven installed to maintain thermoforming sheet properties and to control its aging? 2. If yes, how many hours and temperature level specified for a thermoforming sheet with respective its shelf life? |
| Machine | 1. Preventive maintenance program is deployed for the thermoforming machine? 2. Preventive maintenance program is deployed for thermoforming sheet pre-baking / pre-heat oven? 3. Preventive maintenance program defined for laser trimming / CNC trimming machine? 4. Machine history card specified for thermoforming, pre-heat oven, and trimming machine? |
| Calibration | 1. Calibration of the following critical instruments/sensor is executed? a. Upper and lower heater pyrometer/temperature sensor. b. Thermoforming machine vacuum gauge. c. Pressure gauge of thermoforming machine. d. FRL (filter regulator and lubricator) is calibrated? e. Calibration of timer executed? 2. Calibration of trimming machine sensor/detector executed? 3. Calibration of pre-heat oven temperature sensor executed? 4. Calibration of measuring instrument is executed? |
| Man / Manpower | 1. Skillset matrix maintained for thermoforming machine operators? 2. Thermoforming machine operator trained on operation of thermoforming machine? PLC control? 3. PLC control of the thermoforming machine is access controlled? 4. Password protected, so only authorized personnel can edit / update machine parameters? |
| Method – WI / SOP | 1. Thermoforming process qualification and specification available? 2. Verification and validation of thermoforming process parameters are being followed? 3. Standard operating process/work instruction defined for thermoforming process, trimming process, assembly, and painting process? 4. Thermoforming Following thermoforming process parameters covered in the qualification and specification data sheet? (heater temperature, heating time, vacuum, pressure, cooling time) |
| Measurement – KPI, Quality Control | 1. Thermoforming first piece set up inspection process defined? If yes, first piece inspection records are maintained? 2. Set-up approval is traceable with raw material lot/batch number? 3. Set-up approval is traceable with production lot/batch number? 4. Thermoforming process parameters measured and recorded as per control plan? 5. Risk assessment of Thermoforming process is governed by FMEA? 6. Final inspection of thermoforming products is being conducted? 7. First piece inspection and PPAP activities for thermoforming products are being conducted? |
| Measurement – SPC | 1. Statistical process control (SPC) is followed? 2. If yes, following parameters/characteristics measured and monitored via SPC? (heater temperature, heating time, vacuum, pressure, cooling time) 3. Rejection/rework trained is maintained and monitored by any SPC techniques? |
| Environment | 1. Lux level defined in thermoforming process? Inspection area? 2. If yes, cross check lux level is sufficient and meeting industry standard? 3. Lux level is measured by lux meter? 4. Sufficient light source, accessibility provided for entire thermoforming process? 5. 5S and safety parameters is being followed? 6. Mistake proofing installed for trimming process machine to avoid operator manipulation during trimming operation? |
| Environment – Safety | 1. Fire extinguisher deployed in the shop floor? 2. Fire extinguisher layout defined? 3. Machine maintenance and it’s safe working condition is monitored? |
Feel free to download a free thermoforming process audit checklist (watermarked copy) and use it for assessing the thermoforming process, That’s absolutely fine!
Thermoforming Vs Injection Molding
| Thermoforming Process | Injection Molding Process | |
| Material | Plastic sheet made from extrusion | Plastic resin and master (for color variation) |
| Process | Heating and forming by vacuum or pressure | Melting plastic resin & injecting molten plastic at high pressure in to mold |
| Tooling Cost | Comparatively lower tooling cost | Comparatively higher tooling cost |
| Process Control | Heater temperature, vacuum or positive pressure, cooling time, | Barrel temperature, barrel pressure, mold holding time. |
| Material Wastage | Comparatively higher material wastage during trimming and cutting operation. Higher scrap volume | Efficient material usage as material is only wasted in gates. Lower scarp volume. |
| Family Molding | Family molding possible for bigger size parts | Family molding possible for smaller size parts. Multi cavity molding feasible |
| Production Rate | Suitable for low volume components | Suitable for high volume & mass production |
| Application | Car dashboard, car door trim, car bumper | Car A,B & C trims, brake fluid reservoir Plastic Bottles (injection blow molding) |
| Quality Control Tools | TQM, FMEA, Control Plan, First piece inspection, mold loading and unloading, 5S system, number of forms / mold | TQM, FMEA, Control Plan, First piece inspection, mold loading and unloading, 5S system and number of shots / mold |
Few Key Manufacturers of Thermoforming machines
Conclusion
On the behalf of all the points discussed, thermoforming can be considered as one of the prime factors in the manufacturing industry. Thermoforming has a great scope in the upcoming generation to lead the whole industry and can be the most demanded manufacturing process in the future.