How to design a plastic part13.01.2021
The Plastic Forming & Manufacturing Process: Top 7 Techniques
Jan 05, · Example of radiused corners on the design of a plastic part. Keep in mind that radiused corners should maintain same wall thickness, which means that if Author: Jaycon Systems. Dec 29, · Snap Deflection is not enough. Select plastic material with high permissible strain. Increase snap length. Reduce snap cross section thickness. Estimated Reading Time: 6 mins.
Receive industry related information about product development and manufacturing straight to your inbox. Here are the seven most common methods, and what you need to know to decide which one is best for your next project. Injection molding uses a mold or die made how to design a plastic part aluminum or steel. The mold consists of a core side and a cavity side that is placed into a plastic injection molding machine.
Blower molding made with large capacity molding machine from Semco Plastic Co. The advantage of PIM is that millions of identical parts can be made quickly, with excellent surface finish and at low cost. Molds however can be expensive and complex, depending on the part geometry. Careful engineering design of the mold is required to prevent defects and optimize part parh and processing speed.
Rotational molding also uses a core and cavity mold tool, but the manufacturing process is quite different. Plastic powder is poured into the cavity of the mold, and the mold placed in an oven. While being heated, the mold is slowly rotated on two axes. Gravity is used to stick the plastic to the tool walls and build up the correct thickness.
Rotational molding is how to make semi dried tomatoes at home for large containers with thick walls. Then, the mold is removed from the oven and slowly cooled to prevent warpage.
Full cooling can take several minutes, after which the tool is opened and the part removed for the next cycle. Rotational molding is ideal for making large, hollow or concave shapes, often for vesign use like canoes and tubs.
This is the most common way to make thin-walled, inexpensive containers like disposable drinking cups or bottles. Extrusion molding is used for plastic bottles. Molten plastic in the form of a large droplet, called a parisonis placed into a two-piece clamshell mold.
After the mold closes, the parison is inflated like a balloon until it fills the empty cavity. Because the walls of the mold are water- cooled, the plastic quickly solidifies and the bottle can be ejected. During injection blow molding, gas pressure is used to force molten resin into a mold cavity. The process is easily controlled and repeatable, and is commonly used for transparent plastic drinking bottles.
PET polyethelene terephthalate or PEEK polyether-ether-ketone are the typical choices resin choices for drinking bottles, due to their clarity and durability, and because how to design a plastic part are rated as safe for consumables. They are also easily recycled. RIM is most often used in the automotive industry because it produces lightweight parts that have a rigid skin. This skin is easily painted to make body panels, dashboards and other car parts.
Instead this process requires thermosetting plastic. Rotational molding was used for this lightweight aircraft door. Courtesy RIM Mfg.
Thermosetting plastics undergo an irreversible chemical reaction inside the mold. This usually causes them to ro like a foam, filling a mold cavity. When the chemical reaction is done the plastic sets into its final form. Tooling costs for prototypes are relatively low, while production tooling is moderately expensive. The main cost is in the material, bearing in mind that the resulting desibn must always be finished, usually with a urethane-based gel coat or by painting, so the process is more labor intensive which increases the piece price.
Vacuum eesign is a great choice for making a small number of high-quality rapid prototypes without a big investment in tools or material.
Polyurethane vacuum casting was used to make this case at Star Rapid. When the master is removed, a cavity is formed inside the mold that can now be filled with plastic resin to form a copy s the original. Vacuum pressure is used to pull air out of the mold so that it fills completely with no air bubbles. In this process, the surface finish quality and detail are excellent and pourable resins can imitate many engineering grades what are calculi formed from plastic.
But the molds are not durable and will degrade after 20 or so copies. This is a type of vacuum forming, where thin or thick gauge plastic sheet is placed over a die, heated to a temperature that allows the material to become pliable, then is stretched over the surface of what does it mean when a guy cuddles with you die while vacuum pressure pulls the sheet down and into its final shape.
Thermoforming is useful for clamshell packaging. This process can also be done with simple dies and very basic equipment. Only thermoforming plastics are suitable for this process.
The raw material is pre-heated and placed inside the open cavity of a die. A cap or plug is used to close the die and apply heat and pressure, causing the plastic to cure. This process is great for rubber keypad switches, gaskets, O-rings and other soft, pliable thin-walled parts.
Silicone rubber O-rings made with compression molding. Star Rapid offers a variety of solutions to help you get exactly the plastic or rubber parts that you uow for your project. Contact us today for more information and a free quote. He is passionate about writing and about developments in science, manufacturing and related technologies. He is also a certified English grammar snob. Request a Quote. Subscribe to Our Newsletter Receive industry related information about product development and manufacturing straight to your inbox.
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Plastic powder is poured into the cavity of the mold, and the mold placed in an oven. While being heated, the mold is slowly rotated on two axes. Gravity is used to stick the plastic to the tool walls and build up the correct thickness. Rotational molding is best for large containers with thick walls. Blow molding is a manufacturing technique used to create hollow plastic parts by inflating a heated plastic tube inside a mold until it forms into the desired lovestoryen.comted Reading Time: 8 mins.
Snap fit joints are one of the best and cost effective solutions to assemble plastic parts. Plastic products without screws or welding are joined using snap fit joints. In this article we will discuss how to design snap fit joints for injection molded plastic parts? A snap fit joint consists of a protrusion in a flex plastic wall.
When force is applied, the flex part gets deflected and goes inside the depression during assembly with the mating part. Plastic snap joints have following advantages compared to other types of joints used in plastic parts. Most snap joints used to join plastic parts are cantilever snap joints. One end of the cantilever snap joint is fixed. Whereas the other end is protruded out.
They work similar to the cantilever beams. When the force is applied to the joint, flexible length deflects and catches in the depression of the mating part.
During deflection maximum stress acts at the root of the joint. This Stress can be calculated using classical beam bending theory. For smooth assembly of cantilever snap, entrance angle is provided at the entry side of the snap. Lower the entry angle, lower will be the force required to engage the snap. If the entry and exit angle in entry and exit side are equal. Same amount of force will be required to engage and disengage the snap joint. This is done to ensure that snaps are easy to enter but difficult to remove.
Maximum snap deflection is the required deflection a snap needs to have to engage with the mating part without any failure. During snap design calculation this is a very important factor and it needs to be calculated with the required Factor of Safety. As discussed above, Cantilever snap design works similar to cantilever beam with a point-applied load.
During snap design calculations, maximum snap deflection corresponding to allowable strain in the cantilever beam is calculated using beam theory. From maximum beam deflection and Snap structure, force required for assembly and disassembly of the cantilever snap joint can also be calculated. Maximum cantilever snap deflection in a uniform cross section snap is calculated similar to the deflection of a uniform cross section beam.
According to Beam Theory. This helps in increasing snap deflection while keeping snap structure intact. Snap mating force is the force required to engage the snap joint.
Mathematically it is equal to the multiple of snap deflection force and frictional force. Maximum permissible strain value is a property of a material. It can be calculated if the value of young modulus of elasticity and max permissible stress values are available. This value is also available in the material datasheet. Read this article for more details on strain in mechanical. Annular snap joint is used to join symmetrical round parts.
Depending on annular joint geometry, joints can be removable, permanent or difficult to remove. Complex plastic tooling is required to make parts with annular snap joints.
Following are the common problems faced during snap design and product lifetime. These problems can be solved by designing plastic parts smartly. Small snap deflection or overlap and high strain values is a common problem faced during snap design. This problem can be solved by following ways.
Out of these options, changing material is not a smart choice just to solve the snap deflection problem as very limited material options are available. Whereas increasing snap length can have an impact on product size. Therefore Reducing snap thickness gradually is a good option.
Because it will increase snap deflection with no impact on snap structural integrity. During snap assembly maximum stress acts at the root of the snap joint. Therefore to reduce stress concentration, a generous root radius is provided on snap bottom. During snap design, designers should ensure that even in the worst conditions there is always a clearance between mating parts. It is done to ensure that the snap is always in a relaxation state. We will keep updating this article on various types of snap joint.
If you need any support in plastic parts snap designs or have any questions. Write us in the comment box.
Blog For Engineers and Hobbyist. Cantilever Snap Fit Joint 2. Advantages of Snap Fit Joints. Simple and reliable. Improved Aesthetics : Product looks clean because fasteners are not visible from outside. Reduced number of parts: No additional fastener such as screw is not required.
Reduced Assembly Cost : Snap Joints are easy to assemble and assembly time is also less. Reduced unit part cost : Since fasteners are not required. Overall product cost reduces. Temporary joints : Snap joint parts can be disassembled without damaging parts.
Permanent Snap Joints are also feasible. Disadvantages of Snap Fit Joints. Here are the disadvantages of using snaps to join plastic products: When sliders and lifters are used to create snap features in plastic parts. Injection mold cost and part complexity may increase. Complete part needs to be replaced if even one snap gets damaged. It is always recommended to do snap design according to snap design guidelines for easy assembly, removal and avoid overstress problems.
Snaps are not as strong as screws. Design of waterproof enclosure with snap joints is a challenge and may require various iterations. Types of Snap Fit Joints. Following three types of snap fit joints are widely used to join plastic parts. Cantilever Snap Fit Joint. Cantilever Snap Fit Joint Design. Terminology Used in Cantilever Snap Joints.
Cantilever Snap Fit Joint Calculations. Snap Mating Force Calculations. Permissible Strain Values for Plastic Materials. Cantilever Snap Calculator. Annular Snap Joint. Annular Joint. Common Problems in Snap Fit Joints. Snap Deflection is not enough. Select plastic material with high permissible strain.
Increase snap length Reduce snap cross section thickness. Stress Concentration. Root Radius Recommendation. Stress Relaxation. Stress Relaxation in Snap Joint. Thanks for your valuable feedback. We accept this error. Now its corrected. Add a Comment Cancel reply Your email address will not be published. E-Mail required.