Xometry offers the highest quality HDPE injection molding service and is able to assist with the design of the part and tooling to ensure it follows DFM (Design for Manufacturing) best practices. This will help ensure the product can be successfully manufactured with no defects. Thereafter, Xometry can facilitate manufacturing with one of our trusted partners to ensure the parts are produced to the required specifications. HDPE is a popular injection molding material as it has excellent processability. HDPE also has a low moisture absorption rate and is lightweight, making it ideal for a wide range of applications.Â

Remedies: Place the mold in a machine that utilizes the 20% to 80% rule. This states that, ideally, a barrel should be sized such that 50% of the capacity is used every shot, but based on heat sensitivity of the material being used, that ratio can be between 20% for most materials and 80% for heat sensitive materials. This formula allows enough time for the material to absorb heat properly before being molded.

HDPE is a thermoplastic. It can be remelted and reused if properly processed at a recycling plant. Most recycling plants will accept HDPE due to its widespread use, in addition to HDPE being one of the easiest plastics to recycle. HDPE can also be downcycled, i.e., reused on lower-value items like imitation plastic lumber.Â

Remedies: Increase the injection pressure or speed. While these two parameters are related, it is not proper to adjust them both at the same time. Adjust them each independently and monitor the results closely to determine whether or not the other needs adjustment. As a rule-of-thumb, it is best to make adjustments in increments of no more than 10% of the original setting.

Remedies: Utilize a material that has the stiffest flow possible without causing non-fill. Contact the material supplier for help in deciding which flow rate should be used for a specific application.

HDPE is susceptible to environmental stress cracking. When exposed to long-term tensile loads, cracks can form in the material. This is further exacerbated if the HDPE is exposed to a corrosive environment. These cracks can develop at loads much lower than the tensile strength of the material.Â

Choose from millions of possible combinations of materials, finishes, tolerances, markings, and certifications for your order.

Injection molding HDPE requires a large amount of initial capital investment as the tooling can be very expensive. It is only cost-effective for larger production volumes. Listed below are two potential alternatives to HDPE injection molding:

Remedies: Increase the back pressure to increase the melt temperature and improve the ability for the fronts to flow. This is best accomplished by starting at the minimum of 50 psi and increasing in 10-psi increments until the proper flow is attained. Do not exceed 300 psi. The higher the back pressure the hotter the plastic, and excessive back pressure will thermally degrade the plastic.

Remedies: Inspect the non-return valve mechanism and replace worn or damaged components. This wear is normal but is accelerated by molding materials that have reinforcements (such as glass) in them. The valve should be inspected at least every three months.

Remedies: Vent the mold by grinding thin (0.0005''-0.002'') pathways on the shutoff area of the cavity blocks. The viscosity of the plastic being molded determines the depth of the vent. Stiff materials can utilize deeper vents but fluid materials require thinner vents. In either case, the concept is to remove air from the mold as fast as possible with as deep a gate as the material viscosity will allow.

Remedies: It is best to use an automated system that replenishes material in the hopper as it is used. That way the machine will never run out of plastic. If manual systems are utilized instead, the employee in charge must understand the importance of keeping the hopper filled. Alarm units can be used to emit an audible signal when the material in the hopper reaches a preset level.

High-Density Polyethylene (HDPE) is a thermoplastic polymer supplied in pellet form for injection molding. HDPE is widely used for injection molding due to its low cost, chemical resistance, high tensile strength, impact resistance, and low moisture absorption. In addition to its physical properties, HDPE has excellent processability due to its relatively low melt temperature and low viscosity.Â

Remedies: Decrease the feed throat temperature. The material supplier can provide the proper temperature value for a specific material. Make sure there is no obstruction in the water line used for cooling the feed throat.

Plastic bottles are one of the most popular uses for HDPE. While most bottles are formed using blow molding techniques, the blank tubes used to make these bottles must be injection molded. HDPE does not leach into the stored liquid and is highly moisture-resistant, making it ideal for bottling applications.Â

Short Shots and/or Non-fill can be defined as an incomplete molded part caused by insufficient material injected into the mold. Non-fill can be an extension of a flow line or knit line condition.

Remedies: Increasing the barrel temperatures will allow the flow fronts to stay hotter longer and complete the filling of the mold. Make sure the proper profile is being used and that the material heats progressively as it travels through the barrel from rear to front.

Remedies: Examine the gates and runners to determine if any burrs or other obstructions exist. If possible, perform a computer analysis to determine the proper sizing and location of gates and runners. Ask the material supplier for data concerning gate and runner dimensioning for a specific material and flow rate.

Remedies:  Relocate, or redesign, the gate so that the molten plastic is directed against an obstruction such as a core pin. This will cause the material to disperse and continue to flow instead of slowing down.

Remedies: Increase the mold temperature to the point at which the material has the proper flow and packs out the mold with maximum fill. Start with the material suppliers recommendations and adjust accordingly. Allow 10 cycles for every 10-degree change for the process to re-stabilize.

Hard hats must be able to withstand sudden impacts and must also absorb as much of the impact energy as possible. As such, HDPE is an excellent choice for hard hats as it is a highly durable and impact-resistant material.Â

HDPE is highly resistant to moisture ingress. Also, with the addition of UV (ultraviolet) stabilizers, HDPE can be made resistant to UV radiation, making it an ideal material for outdoor applications.Â

HDPE has poor UV resistance as the carbon-hydrogen bonds are attacked by UV radiation. The breaking of these bonds ultimately causes photo-oxidation which degrades the material over time. Additives like UV stabilizers can be incorporated into the HDPE formulation to improve its UV resistance.Â

HDPE has low thermal conductivity. If cooling is too quick or uneven, this can result in the part warping or shrinking during injection molding. HDPE can have a shrinkage rate of between 1.5% and 4.0%.

Remedies: If possible, run the machine on the automatic cycle, using the operator only to interrupt the cycle if an emergency occurs. Use a robot if an ``operator'' is necessary. In addition, instruct all employees on the importance of maintaining consistent cycles.

HDPE is considered food-safe and is approved by the FDA. It is widely used for both single-use and long-term food storage applications. In addition, HDPE is very tough and can protect the food contents during transportation.Â

HDPE has a density of around 960 kg/m3. This is lightweight compared to metals and even some plastics. HDPE also has a high strength-to-weight ratio which means it can be used to produce thin-walled products like bottles or chemical tanks but still maintain high levels of strength and rigidity.

HDPE is a popular material for garden furniture due to its low cost. The strength and toughness of HDPE make it possible to produce lightweight and low-cost furniture without compromising mechanical strength. HDPE can also be downcycled for use in imitation lumber that can be used to produce low-cost furniture.Â

Each HDPE formulation will have a unique set of material properties depending on their intended application. Table 1 below lists some common material properties of standard HDPE:

HDPE is highly resistant to moisture and is relatively flexible. As such, it is widely used for piping to transport large volumes of water. Individual pipe sections are welded together to eliminate potential leaks. These pipes are often buried underground.Â

Get custom HDPE injection molded prototypes and production parts in as few as five business days. Dozens of materials and finishes are available. ISO 9001:2015, ISO 13485, IATF 16949:2016, and AS9100D certified.

HDPE is considered a commodity plastic and is relatively low-cost when compared to other plastics like polypropylene, for example. This makes it a cost-effective material to use for injection molded products. It must, however, be noted that the tooling required for injection molding is often the largest contributor to initial set-up cost.Â

HDPE is considered food-safe by the FDA (Food and Drug Administration) and is widely used to store food items. HDPE is highly inert and stable and as such does not leach dangerous chemicals into food products.Â