7. Draft angle orientation
When we begin detailing a concept and transforming it into a production injection molded part, draft angles must be added to all surfaces in line of draw. In most cases the draft orientation is obvious. However, there are instances where the draft can be oriented toward the core or cavity. These decisions affect parting lines, tool design, fits between parts and cost. There are instances where the location of the parting line could unnecessarily complicate the mold and increase tooling cost. Reviewing these details with a molder during the development process will ensure that the design has been optimized for minimal cost and optimal performance when it is transferred to the molder for production.

8. Texturing and draft
Experienced designers and engineers familiar with plastic injection molding are well aware of the effect surface finish has on draft angles. High gloss smooth surfaces can be ejected from a mold much easier than a rough or textured surface. There are numerous instances during the detailing of production parts where designers must minimize draft angles or specify textures on exterior surfaces. For example, core pins and bosses may require a ½° draft or less to eliminate potential sink marks. Core pins with minimal draft should be polished for easy part ejection. The same is true for ribs or other features that are typically internal to a part.
On external surfaces, specific textures usually are etched into the steel to a certain depth. Deep textures are sometimes specified for a desired effect. Generally, exterior surfaces should include 1°draft for each mil of textured depth in addition to a starting draft angle of 1°. Although this basic rule appears straightforward, there are instances where the texture may have to bleed off on surfaces where the draft cannot comply with these requirements. It is advisable to discuss these requirements with a molder to ensure that the parts comply with the aesthetic and functional requirements of the design.

(source:https://www.hthc-tech.com/injection-molding-design-the-10-keys-to-success-2/)

5. Gate location
Gate location of Consumer Electronics plastic parts ideally should be specified by a designer, molder and tool maker. Gate location is critical to virtually every attribute of an injection molded part. It affects appearance, warpage, tolerances, surface finish, wall thickness, molded in stresses and physical properties, to name a few.
Some designers use mold flow simulations to dictate gate design and location. I think that’s great if the molder agrees with their recommendations. I disagree with designers who insist that their gate recommendations must be maintained without compromise. In either case, close collaboration with a molder throughout the design cycle will ensure that the gate will not adversely affect part performance, appearance or fit. Molders are also willing to advise designers about the type of gate and features that may have to be added to the part geometry based on gate design. Molders also will offer trade-offs between different types of gates, including fan gates, edge gates or sprue gates.

6. Shut-off angles
Most readers will be familiar with the terms “shutoff angle” and “bypass.” These terms refer to the minimum angle between the core and cavity, which typically creates an opening in a part that would otherwise require a slide or cam. Features such as circular holes, snap locks or large rectangular openings can usually be molded in walls perpendicular to the line of draw by designing features for a bypass in the mold.
All molders want as much angle between the core and cavity as possible, whereas designers typically want no angle or minimal angle in these features. The compromise usually lies between a minimum of 3° to 5° in most cases. Benefits of discussing these details with a molder or tool maker cannot be over emphasized. Many hours will be saved before you waste your time detailing part features in CAD with lengthy feature trees that are difficult to edit after the part has been fully detailed. Some molders will accept a 3° minimum angle, while others may require a minimum of 8° to 10°. The longevity of the tool, tool quality, mold steel specifications and materials being molded all will affect these details.

(source:https://www.hthc-tech.com/injection-molding-design-the-10-keys-to-success-1/)

3. Sink marks
Experienced designers are always faced with the challenge of avoiding sink marks in injection molded parts. Although the recommended maximum wall thickness at the base of a rib or boss should be less than 60% that of the perpendicular face wall, some molders prefer 50% or less. It should be noted that this is a guideline and not a guarantee that the part will be acceptable to the QC department.
Cosmetic surface imperfections are dependent on gate location, tool quality, nominal wall thickness, material, additives, surface finish, color and viewing angle. Production problems can be avoided by clearly establishing acceptable surface quality with the molder well before any of these decisions are made. Reputable molders will provide honest expectations and backup plans well before production starts. Molders may suggest eliminating all features on the inside of a part, while others may suggest special coring techniques.
4. Steel safe areas
When we are designing injection molded parts, we’re often faced with details requiring tight tolerances such as snap fits, alignment features or interlocking parts. It’s easy to perfectly align and match these features in CAD, but it’s not that easy to repeatedly produce them during production. Details that cannot be confidently reproduced by a molder are often designed “steel safe.” For the benefit of those not familiar with the term, steel safe means the design feature is detailed with enough clearance to allow a tool maker to easily machine away steel in the mold to tighten up the clearances after initial test shots are molded. Most molders prefer these precautionary measures to avoid welding material back into the mold, which is then later machined.
Welding always compromises tooling quality, is expensive and delays production startup. Close collaboration with a molder or tool maker early in the design process will minimize revisions in your design, enabling both of you to agree on critical dimensions that should be made steel safe and on the amount of clearance to include in the design. Typically, these cooperative, well-planned decisions add little or nothing to the tooling budget and have a minimal effect on production launch. Conversely, some molders want custom plastic parts designed exactly as expected and don’t want added clearance. That’s why close communication with your selected molder is important.

(source:https://www.hthc-tech.com/injection-molding-design-10-critical-considerations-for-designing-high-quality-molded-parts-3/)

It should be noted that designing a quality injection molded part requires a designer to be knowledgeable about all the fundamental design parameters associated with custom plastic injection molding and to be highly skilled in the art. The molder/designer partnership is not intended to be an internship program—it is supposed to optimize handoff of the final design to production with few or no changes. If completed successfully, final production parts typically are cost effectively molded precisely to specifications for the following reasons.
1. Material options and consequences
Materials are often specified early in the design process and should be mutually agreed upon by both parties. Sometimes molders may purchase large quantities of specific resins at major discounts. These discounts can be passed on to customers. For example, if a designer can specify an ABS grade that matches the properties of one purchased in large quantities by a molder, many tens of thousands of dollars can be saved. A designer may discover certain high-performance resins may not be ideally suited for a molder due to viscosity, high glass content or crystallinity. A resin may be chosen for specific physical or chemical-resistance properties but may be very difficult to mold or maintain specified tolerances. Molders should be in agreement with specified resins and overall part requirements, since they will be required to actually mold the parts.
2. Critical tolerances
One of the greatest challenges for any designer faced with designing an injection molded part is providing enough clearance in the design for tolerance variation. Tolerance variation depends upon several variables, including materials, process control and tool design. Acceptable tolerance ranges in a design will vary greatly from one molder to another. It’s imperative that designers discuss reasonable critical tolerance specifications with a molder and consider options for possible mold revisions, if required. This may require certain design features to be intentionally designed with extra clearance, which will later be tightened by removing steel from the mold. No one wants to add steel with welding to remedy interference problems. Molders may offer a number of suggestions for maintaining tight tolerance control, including post machining, fixturing and gate locations.

(source:https://www.hthc-tech.com/injection-molding-design-10-critical-considerations-for-designing-high-quality-molded-parts-2/)

There are thousands of designers who design injection tolling plastic parts but there is an elite group within this large community who can actually design parts for injection molders. Injection molded product design evolves through many phases of development before all the parts are ultimately documented and released to a molder for production. This last step in the development process is the most critical, since design changes or corrections can no longer be made without significantly adding cost or project delays.

Unfortunately, plastic part design mistakes will be uncovered only after first article parts are inspected and evaluated by the project team. Even with today’s sophisticated mold flow simulation, 3D CAD interference checks, rapid prototyping and numerous other development tools, it is impossible for anyone to predict every potential problem for an injection molded part. However, there is a very simple, low-cost method for minimizing potential problems and virtually ensuring perfect parts. It’s called partnering with your molder, which is the focus of this article.

It doesn’t matter how well you think you know how to properly design parts for plastic injection molding—you should always form a close partnership with your preferred molder as early in the design process as possible. Every molder has his or her own tooling preferences and techniques for molding parts, which can have a significant effect on part design. These subjective preferences can influence any of the following major design-related parameters affecting an injection molded part:

1. Material options and consequences
2. Critical tolerances
3. Sink marks
4. Steel safe areas
5. Gate location
6. Shut-off angles
7. Draft angle orientation
8. Texturing and draft
9. Scheduling of critical start-up phases
10. Secondary operations and fixtures

(source:https://www.hthc-tech.com/injection-molding-design-10-critical-considerations-for-designing-high-quality-molded-parts-1/)

Plastic injection molding is extremely versatile method of producing parts and products. It is one of the preferred methods for manufacturing parts because it has multiple advantages over other methods of plastic molding. Not only is plastic injection molding simpler and more reliable, it is also extremely efficient. You should have no doubts about using this method to manufacture parts.

Here are 5 major advantages of using custom plastic molding for manufacturing plastic parts and components.

1. Detailed Features and Complex Geometry

The injection molds are subjected to extremely high pressure. As a result the plastic within the molds is pressed harder against the mold compared to any other molding process. Due to this excessively high pressure, it is possible to add a large amount of details into the design of the part.

Furthermore, due to high pressure during the molding process, complex and intricate shapes can easily be designed and manufactured which otherwise would have been too complicated and expensive to manufacture.

2. High Efficiency

Once the injection molds have been designed to the customer’s specifications and the presses pre-programmed, the actual molding process is very quick compared to other methods of molding. Plastic injection molding process hardly takes times and this allows more parts to be manufactured from a single mold. The high production output rate makes plastic injection molding more cost effective and efficient. Typically, hot-runner ejection mold systems produce parts with more consistent quality and do so with faster cycle times, but it’s not as easy to change colors nor can hot runners accommodate some heat-sensitive polymers. Learn more about the key differences between hot-runner and cold-runner systems.

3. Enhanced Strength

In plastic injection molding, it is possible to use fillers in the injection molds. These filler reduce the density of the plastic while it being molded and also help in adding greater strength to the part after it has been molded. In fields where parts need to be strong and durable, plastic injection has an option that other molding processes do not offer.

(source:https://www.hthc-tech.com/5-major-advantages-to-using-plastic-injection-molding-for-the-manufacturing-of-parts-part-a/)

Point-of-purchase display components require rugged construction in combination with an attractive appearance. At Huitong, we injection molded a range of products, including items such as Home Appliance plastic parts, Automotive Parts plastic parts, and product stops for one of the leading companies in the point-of-purchase display industry. This project highlights our ability to provide value-added services in conjunction with close tolerance plastic injection molding that equates to cost savings over the entire product lifecycle.
Working with the customer supplied prints, we first focused our attention on mold design. Our goal, as always, was to construct molds that would lead to volume high quality while minimizing production costs. By paying detailed attention to aspects such as cavity dimensions, gate location, venting, cooling systems, and more, we achieved optimal cycle times while upholding tolerances as close as ± 0.005” across varying complexities in part geometry. One critical feature of these parts was a fine quality surface, so we leveraged the capability of our EDM equipment. This allowed us to create a very fine finish on the mold cavities to add clarity and quality to the surface of the finished part with no extra processing required.

(source:https://www.hthc-tech.com/plastic-injection-molded-display-components/)

Injection molds must have a high precision match between the two mold halves in order to perfectly control the material flow. Creating the mold is crucial to building a seamless, precision product.  Injection molds are typically constructed using steel or aluminum, and precision machined to form the features of desired product.
The injection molding process is fairly repetitive once a functional, errorless mold has been produced. It also has a low scrap rate relative to other manufacturing processes such as CNC machining which cut away considerable portions of the original material blank in a subtractive process.
The Plastic Injection molding process is highly repeatable and reliable for high volume production. Once the first part is produced, the second is going to be practically identical, due to the ability to make multi-cavity injection mold parts, where multiple parts are made with one cycle. Other advantages are the wide range of material selection, low labor costs, minimal scrap losses, and minimal requirements to for post-molding finishing operations.
The major disadvantages of injection molding are the initial costs of the mold design, which tends to be high due to design, testing, and tooling requirements and the longer required lead times. Some custom complex parts may encounter problems during the injection molding process such as warpage or surface defects. Therefore, injection molded parts must be designed with careful consideration to any change in geometry as they cool and the material selection to assure stability.

Conclusion

The process of injection molding may seem like a complex one, but it’s the most common manufacturing method because of its capability and efficiency to produce a plethora of custom plastic parts. Injection molding is one of the most cost effective ways to build both functional prototypes and end use products.

(source:https://www.hthc-tech.com/how-does-plastic-injection-molding-work/)

Overall toughening process of mold

Main causes of material failure are stress concentration and fatigue fracture when it comes to produce office equipment plastic parts. In order to increase toughness, reduce brittleness and fracture of ordinary cold work die steel, low temperature quenching and low temperature tempering process can be used; high temperature quenching and high temperature tempering process can significantly enhance toughness and thermal stability of hot work die steel. When mold cavity is large and wall is thin, upper limit of normal quenching temperature is required to increase amount of retained austenite so that mold does not swell. Rapid heating method has a short heating time, a reduced tendency to oxidative decarburization, a small grain size, quenching deformation of large tool of carbon tool steel is small. High-speed steel adopts low quenching and high-returning process, quenching temperature is low, tempering temperature is high, which can greatly improve toughness. Although hardness is reduced, mold can be improved in resistance to fracture and fatigue damage. In order to reduce residual stress, mold should be tempered after quenching. Effect of tempering is to release material due to internal stress generated by quenching in a short time. Tempering should be sufficient, and tempering is insufficient to cause pre-grinding cracks.

Surface strengthening heat treatment process of mold

It has been found that wear and adhesion occur on surface of mold, common fatigue and fracture often start from surface. In order to improve life of mold better and make better Custom Plastic Parts, it is necessary to enhance wear resistance of surface of part, and surface strengthening treatment of main forming parts is the most direct way. Surface strengthening process of mold mainly includes gas nitriding, ion nitriding, electric spark surface strengthening, boronizing, thermal diffusion carbide coating, chemical vapor deposition, physical vapor deposition, laser surface strengthening, ion implantation, plasma spraying, and so on. In actual production, different surface strengthening processes are adopted according to different uses of mold. For example, in order to enhance wear resistance and compressive strength of surface layer of blanking die for mold manufacturers in china, a strengthening method such as electric spark or hard alloy surfacing may be adopted; for surface of hot working die (die-casting mold, plastic mold), nitriding method may be used to enhance wear resistance, heat fatigue resistance and corrosion resistance; drawing die and bending die are mainly wear caused by friction in production, and sulfur permeability process can be used to reduce friction coefficient in order to enhance wear resistance of material. Carbonitriding is suitable for surface strengthening of various types of molds. PVD and CVD in surface coating hardening technology have made great progress in recent years. Vacuum evaporation, vacuum sputtering and ion plating are commonly used in PVD. Among them, ion plating has strong adhesion, fast deposition speed, no pollution. Etc. Ion plating process can plate tic and TIN on surface of mold, and its service life can be extended several times to several tens of times.

(source:https://www.hthc-tech.com/analysis-of-methods-to-improve-service-life-of-molds-4/)

Reasonable formulation of forging specifications for die steel

Mold materials for making home appliance plastic parts are mostly high-carbon, high-alloy steels, and there are defects such as composition segregation, tissue segregation, and carbide segregation exist in varying degrees, which cannot be directly used for molding. At the same time, shape and size of raw materials used are difficult to match with module, forging is an indispensable means of obtaining required internal organization and performance, reducing amount of machining. Through forging can effectively improve carbide segregation of tool steel, and generally can reduce carbide segregation level 2 after forging, up to level 3.
Die steel generally has poor thermal conductivity, and heating speed must be slow and uniform. Large forgings generally use preheating or step heating to control heating speed. Position of steel in furnace should be appropriate, and sometimes it should be repeatedly turned over so as to make heat as uniform as possible. In order to maximize breaking and uniform carbide, it is necessary to adopt a deformation process in which pier is thick, long and repeated repeatedly, and finally, like kneading dough, it is turned up and down, front and back, left and right, so that internal deformation is sufficient and uniform. After billet is forged, it should be slowly cooled with furnace or cooled in a hot ash box. However, for Cr12 steel, if it is slowly cooled after forging, it is easy to precipitate network carbide on grain boundary, thus affecting quality of blank. Therefore, it should be quickly cooled to about 700℃, then pit cold or into furnace slow cooling. Forgings should minimize number of forging fires to control oxidation and decarburization of billet.

Select a reasonable mold heat treatment process

There are many ways to improve performance of mold to produce excellent medical products plastic parts. Use of new heat treatment technology is a cost-effective and effective way. Mold heat treatment process mainly includes matrix strengthening and surface strengthening treatment; strengthening and toughening of matrix is to strengthen toughness and strength of matrix, reduce occurrence of fracture and deformation. Surface strengthening is mainly to increase wear resistance, corrosion resistance and lubrication properties of surface.

(source:https://www.hthc-tech.com/analysis-of-methods-to-improve-service-life-of-molds-3/)