Blow moulding, also known as blow forming, is a manufacturing process by which hollow plastic parts are formed. It is a process used to produce hollow objects from thermoplastic material. Typical products include consumer bottles, fuel containers, automotive reservoirs such as required for windshield washer fluids, small recreational boats such as kayaks and also mannequins and many other products with complex, freeform shapes.
There are three main types of blow moulding:
- extrusion blow moulding
- injection blow moulding
- stretch blow moulding
The blow moulding process begins with melting the plastic from a pellet form and forming it into a parison or ‘preform’. A parison is a tube-like piece of plastic which is extruded between the mould cavities. The machine then closes to pinch the parison and blow it to the shape of the cavities. A preform is typically injection moulded with a hole in one end in which compressed air can pass through to blow or stretch the plastic to match the shape of the cavities.
The basic process has two fundamental phases. First, a preform (or parison) of hot plastic resin in a somewhat tubular shape is created. Second, a pressurized gas, usually air, is used to expand the hot preform and press it against the mould cavities. The pressure is held until the plastic cools, once the plastic has cooled and solidified the mould opens up and the part is ejected.
Advantages of 3D scanning or 3D digitizing technology for blow moulding
Today’s advanced 3D scanning systems coupled with 3D modeling and 3D inspection software have become powerful tools for accelerating product launches by saving time with both product design and tooling development while offering faster, more thorough quality inspection. The Steinbichler COMET white light 3D digitizing system combined with PolyWorks Modeler or Geomagic Studio offers the user numerous opportunities to help design and manufacture blow moulded products much faster than in the past using conventional approaches. Some of the advantages of effectively applying 3D scanning technology are outlined below.
Making a new product size
An existing mould or product ‘master’ model is scanned with a Steinbichler COMET white light or T-Scan laser digitizing system. The resulting 3D ‘point cloud’ data is then processed in either PolyWorks Modeler or Geomagic Studio. This 3D data is then converted to a 3D polygon model (typically in STL format) and can be readily scaled up or down to adjust for overall product size. Either constructed rapid NURBs surfaces or cross-sections (typically in IGES or STP format) can be generated and easily exported for use as reference data in a CAD package, where the existing CAD model is modified to the new size or features added or modified as required.
Making a mould based on a prototype
A prototype part or model is scanned with a Steinbichler COMET white light or T-Scan laser digitizing system and then processed in either PolyWorks or Geomagic. Cross-sections, specific features or polygon data are generated and exported for use as reference data in a 3D CAD package to accelerate the final design process. Geomagic Fashion with parametric exchange can also be used in conjunction with a CAD package to quickly build a parametric or ‘hybrid’ 3D CAD model.
Where 3D CAD data does not exist or is suspected of differing from the current tooling, a mould is scanned with a Steinbichler COMET white light system to take advantage of the high data density and excellent data density to capture key product features. A complete surface model can then be constructed using then the new 3D point cloud data in either PolyWorks Modeler or Geomagic Studio to create a precise 3D model of the existing tooling cavities. This process is typically referred to as reverse engineering.
Product and Tooling Inspection
The part or tool cavities (pin and bush) are scanned with a Steinbichler COMET or T-Scan laser system then aligned to the available 3D CAD and inspected using PolyWorks Inspector or Geomagic Qualify. A comprehensive ‘colour map’ style inspection report can be immediately produced to easily visualize deviations between the part and the 3D CAD. Local, numerical deviation values can also be reported for specified inspection points and key features. If the same inspection procedure is likely to be run repeatedly for the same part, the inspection can be automated in the software by writing macros to complete the desired comparisons and analysis.
Selecting the right 3D Scanning System & Software
A wide variety of hardware and software combinations are available to suit your specific manufacturing requirements. The choice of 3D digitizing system is generally determined by the size of the part or tooling and accuracy needs. For example, Steinbichler COMET system is ideally suited for smaller products such as bottles and jugs, while the Steinbichler T-Scan laser system reduces scanning time for larger products.
The Applied Precision Team has extensive experience in applying this technology to blow moulded products and is available to assist you in evaluating the best possible combination of equipment and software for your business needs. Our team continues to be recognized by our customers for excellence in technical support and customer training programs to ensure that you get the greatest possible value from your 3D scanning technology investment.