Understanding Material Hardness: Key Concepts and Applications

The suitability of the material to be used for a part is very important to the part being able to function in its projected environment. One of such materials that determines the suitability of a material to the project is hardness.  It dictates if your project requires a material having high hardness, like steel, or rather soft materials.

We all know that using the wrong materials in a project might bring a disastrous effect, especially when the produced part is part of a larger project. Therefore, it is indispensable to test the hardness of your material before production.

If you need a substance to bear high indentation or abrasion without deforming, then you should pick hard materials. However, high hardness alone may not necessarily make the material eligible for all projects. You will have to consult an expert machining company to find out that, too, can be suitable for your project.

Basic Concepts of Material Hardness

Material hardness designates the resistance of a material to deformation, particularly permanent deformation, scratching, cutting, or abrasion. It accounts for the material’s resistance to wear. Hardness is, therefore, an important property in the choice of material for an application area, beginning from tools for industry to consumer products.

Types of Hardness

The two major types of hardness are surface hardness and bulk hardness. As a matter of fact, bulk hardness and surface hardness can be understood from their nomenclature. Often, it is measured in order to relate the wear resistance of a surface.

The bulk hardness, on the other hand, means an overall measure of the material’s hardness, considering the whole volume. It presents a general idea of the performance that one would expect under stress and pressure. 

Bulk hardness is very important for applications where the structural integrity of the material is put to the test, with heavy loads, without deforming.

Relationship between Hardness and Other Material Properties

Hardness is one of those properties intimately related to others, like the strength, ductility, and toughness, of a material. Toughness, ductility, and strength are nearer relationalities and depend on a harder material. 

Harder material is most often stronger or has more wear resistance, but being harder does not always indicate ductility or vice versa. This simply means that it might turn out to be quite brittle and crack under some conditions.

For instance, high-carbon steel possesses high strength and hardness and is therefore used in cutting tools. However, one of its drawbacks refers to brittleness in cases where resistance to flexibility is required. On the other hand, there are some materials, such as rubber, that present quite high ductility but low hardness and strength.

Hardness in Injection Mold Design

Hardness plays a crucial role in injection mold design. It determines the mold’s ability to withstand wear, pressure, and the high temperatures of the injection molding process. Hardness also impacts the mold’s durability and the quality of the final product.

Selecting Mold Materials Based on Hardness Requirements

Selecting the right mold material based on hardness is essential for ensuring the mold’s longevity and performance. Harder materials, like tool steels (H13, P20), are often chosen for molds subjected to high wear and tear. These materials resist deformation and abrasion, ensuring consistent part quality and reducing maintenance costs.

For less demanding applications, softer materials like aluminum may be used. Aluminum molds are easier to machine and less expensive but have a shorter lifespan. The choice between hard and soft materials depends on factors like production volume, part complexity, and the type of plastic being molded.

Case Studies of Mold Designs Influenced by Material Hardness

In automotive plastic injection molding, Audi Ag faced issues with a mold used for producing large plastic components. The original mold, made from softer steel, wore out quickly, leading to frequent replacements and downtime. By switching to harder tool steel, the mold’s lifespan increased significantly, reducing costs and improving production efficiency.

Another example is in consumer electronics. Apple Inc. used an aluminum mold for prototyping plastic phone cases due to its ease of machining and lower cost. However, for mass production, they switched to a harder steel mold. This transition ensured that the high volume of parts produced maintained consistent quality without frequent mold replacements.

Hardness in Custom Injection Molding

Hardness strongly influences custom injection molding as it impacts material selection and thus eventually the performance of its products. The overall hardness refers to the ability of the product to stand against wear, pressure, and deformation. Right hardness will assure molded parts the required reliability for their entire service life.

How to Choose Plastic Materials for Required Hardness

If a final product has to be of a specific hardness, then the correct plastic materials have to be picked for custom injection molding. Materials like polyethylene and polypropylene are chosen because of their soft properties that will fashion resilient and shock-resistant products. A number of polycarbonates and ABS, Acrylonitrile Butadiene Styrene, are examples of materials used in making harder and more rigid parts.

Material hardness has to be matched according to usage. In other words, softer plastic materials will be better suited to applications requiring flexibility and shock absorption. Harder plastics are best suited for products that have structural needs and endure wear.

Examples of Custom Injection Molded Products with Specific Hardness Requirements

For instance, Medtronic applies it in the production of casings for medical devices. To protect and give long-serving life to the device it covers, housing Sheila requires a hard and resistant plastic, such as polycarbonate. The property of hardness of polycarbonate provides resistance against impact and wear out, especially necessary in medical environments.

Another example is LEGO, which uses ABS plastic in its iconic bricks. The perfect mix of hardness and toughness in ABS gives snaps that hold the bricks together yet are resolute against wear from repeated use. This strength is imperative to holding up that precision and durability for which a LEGO product’s excellence is trusted.

Conclusion 

If you want to select a material that is going to suit your project, then you must carry out an appropriate material hardness test. There are various methods by which you can conduct the hardness test on your material. Consult an expert company for professional advice in relation to the hardness of your material.