September 11, 2023
When it comes to rapid prototyping and manufacturing, CNC machining, 3D printing, injection molding, and sheet metal fabrication have become indispensable. As technologies evolve and adoption of new-age processes gain more currency, resource-hungry and polluting manufacturing practices will be phased out. CNC prototyping, injection molding prototyping, sheet metal prototyping, and 3D printing prototyping have enabled innovators and entrepreneurs to test their product designs and capabilities, using a vast range of materials. Ensuring precision and low wastage, each of these cost-effective, environment-friendly manufacturing processes offer unique benefits.
Let’s take a look at their salient features and cost drivers.
It is an automation-driven manufacturing method that controls the movement and functions of machine tools through pre-programmed computer software embedded in the tools. Used for making metal and plastic parts, sophisticated CNC equipment can perform detailed and complex functions with remarkable precision.
Unlike 3D printing, which is an additive process, CNC machining is a subtractive method. It requires the usage of tools like mills, lathes, routers, electric discharge machines, plasma cutters, laser cutters, drills, grinders, and water jets to transform a work piece/ raw material into a custom-designed product with smooth finish and tight dimensional tolerances.
Process outlining: The process starts with designing a 3D model of the desired object in a computer-aided design (CAD) software to determine the exact dimensions and properties of the output. Based on the 3D model data, the computer-aided manufacturing (CAM) software programs the machine tools for the creation of a prototype or a finished part. In other words, the CAM software uses a language, called the G-code, that the tools understand to turn the 3D design into reality. The CAD-CAM software systems are usually integrated to streamline the manufacturing process.
Advantages: There are several advantages to CNC machining. Since the tools are computer-controlled, there is greater accuracy than manual processes, which are prone to human errors. As a result, it is easy to achieve consistency in the quality of the final products. CNC processes allow for rapid prototyping and faster production, reduced wastage, quick assembly, and efficient use of energy – all of which result in lower production costs and environmental sustainability.
Industrial applications: CNC prototyping and manufacturing have use cases in various key industries such as aerospace, petrochemical, healthcare, marine, transportation, military and defence.
Cost factors: When it comes to quick prototyping and on-demand manufacturing with tight tolerances, CNC machining is considered one of the most cost-effective methods. However, the costs vary widely from a few hundred dollars to a few thousand dollars, depending on the materials, complexity and size of the product, machining costs, volume, and labour.
Materials: The costs of materials are dependent on their availability, properties and overall production costs. Metals cost more than plastics. Titanium is the most expensive of the lot. The common metals used for machining are aluminum, brass, copper, and various kinds of steel. Thermoplastics such as Acrylonitrile Butadiene Styrene (ABS), Nylon 66, Polyetheretherketone (PEEK), and Polycarbonate (PC) are also widely used.
Design, size, and tolerances: Complex geometries increase costs – intricate designs need more material and take a longer production time than parts with simple geometries and standardized features. Design requirements such as non-standard hole sizes, sharp inside corners, wall thickness, lettering, and deep cavities can warrant the use of sophisticated machines, thus driving up expenses. The machining cost, calculated by the hour, also depends on the size and weight of the machine, speed, power, and machine configuration.
Size too has a similar impact on costs; and so does tolerance. Though CNC is preferred for dimensional accuracies, tight tolerances make it challenging for the tools to deliver. It may lead to several machining attempts – depending on the level of precision – resulting in higher charges.
Quantity: The volume of the order affects the cost of the final product. While an increase in the number of finished parts will add to the overall cost, the cost per part will decrease due to economies of scale.
Labour and Post-Processing: The labour cost is primarily for the designer who creates the 3D CAD design model for machining. There are additional charges for services of skilled personnel operating the CNC machine and supervising the production process. Sometimes, manual work is required for assembling, surface finishing, and post processing the parts.
Injection molding is a rapid prototyping and manufacturing process that creates identical parts by injecting molten material into a mold. Versatile in nature, this method is ideal for a high-volume production of the same part at a low per unit cost.
Injection molding prototyping works on various kinds of plastic -- such as acrylonitrile butadiene styrene (ABS), nylon, high-density polyethylene (HDPE), low-density Polyethylene (LDPE), polycarbonate (PC) – metals, rubbers and alloys.
The main criteria for material selection are tensile strength, toughness, bending stiffness, temperature resistance, electrical insulation and chemical resistance. By one estimate there are over 25,000 injection molding materials.
Process outlining: The most important part of the process is to create the mold as per the design parameters. Once the mold is finalised, the raw material -- in powder, pellets or granular form -- is fed into the machine. It is then heated beyond its melting point. The molten, viscous fluid is injected into the mold where it cools and hardens to the configuration of the cavity. Then the mold is opened and the finished part is ejected from the machine. Depending on the size and complexity of the part, it takes 10-90 seconds to complete the cycle.
Advantages: Injection molding is ideal for mass produced products and rapid prototyping. The typical turnaround time is 6 to 10 weeks -- four to six weeks to manufacture the mold and two to four weeks for production and shipping. The parts are strong and durable and the process allows for tight tolerances and outstanding repeatability. The cost per unit is low for high and medium volume production. Wide material options, freedom to create intricate designs, low wastage, environment-friendliness, and very little post production requirements make it a reliable choice for manufacturers.
Industrial applications: Plastic parts have wide applications across different industries due to their versatility. Consumer electronics, medical and pharmaceutical industry, automobiles, food and beverages sector have benefitted from injection molding.
Cost factors: Injection molding manufacturing could be cheaper than CNC machining for product runs in the thousands and tens of thousands. Several factors affect the final price of the parts, including mold creation, the cost of the raw material, and cycle time.
Mold making: The mold cost depends on the size, geometry, and material. Design features such as cavities, texturing, engraving, undercut features, and inserts significantly add to the costs. Molds made of high-quality steel are expensive but they have a longer service life. The creation of the mold can be a complex and labour-intensive process requiring various parts to be assembled together through manual and automatic means. These parts usually have tight tolerances and are made using CNC machining and electrical discharge machining, leading to cost escalation.
Injected materials: Thermoplastics like polypropylene and polyethylene are inexpensive while PEEK, polycarbonate, polysulfone, and teflon are costly. Feedstock (powder) for metal injection molding is quite expensive.
Cycle time: Even a few seconds delay in the injection molding cycle for bulk production has an adverse impact on the financial bottom line. An optimised molding cycle improves the production process, lowers energy and labour costs, and increases profits.
Volumes: Injection molding is cost-effective in large volumes. Otherwise, the cost per unit part tends to be higher.
Labour costs: Though the production process is largely automatic, it still needs trained personnel to design and build the mold, and carry out post-processing functions, product inspection, and packaging.
It is the process of converting 2-dimensional metal sheets into desired 3-dimensional shapes through a series of actions involving cutting, punching, welding, folding, assembling, and finishing, depending on the unique specifications of the end product based on its 3-D design.
Manufacturers typically use stainless steel plate, cold rolling steel, hot rolling steel, copper, brass, aluminium, hot-dip galvanised steel plate, and zinc, as raw materials.
Process outlining: Like any rapid prototyping process, sheet metal prototyping too begins with the designing of a 3D model of the desired object with specifications such as wall thickness, hole orientation, and bend allowance. Next comes the instructions for the machine tools based on the model and the properties of the metal sheet (the raw material). The component’s geometry dictates the changes the sheet undergoes via cutting, bending, punching, stamping, and welding. Surface finishes are essential to improving the product’s aesthetics.
Advantages: Sheet metal output is lightweight, durable, high-quality, and economical than products from traditional manufacturing. The computer-controlled processes ensure accurate dimensions. There is an abundance of materials to work on, which means feedstock usually doesn’t cost much unless there is acute scarcity. The metals can be fashioned into various shapes and are able to withstand extreme temperatures.
Industrial applications: Sheet metal fabrication is extensively used in automotives, consumer products, aviation, and real estate.
Cost factors: Sheet metal prototyping is cost-effective if one keeps in mind the following factors:
Raw materials: Material type, thickness, and grade influence the choice of raw materials. Aluminium and steel are common sheet metals while certain grades of stainless steel are costly. However, the manufacturer should not forget the end use of the product and choose the material accordingly.
Production efficiency: It’s the key to the manufacturing process, with set-up time, cycle time, and scrap rate contributing to costs.
Outsourcing: Manufacturers may need to outsource specific fabrication processes to maintain high quality standards.
Design factor: It’s best to keep it simple and avoid intricate designs. Specialised design elements such as machined pockets and blind holes can drive up costs.
Finishing: Brushing, polishing, powder coating, and plating help in protecting the material and enhancing the appearance of the finished product.
Labour charges: Sheet metal fabrication is a labour-intensive process, requiring skilled craftsmen. Optimal utilisation of labour is essential for cost control.
It is the process of rapid prototyping, manufacturing a 3D object, layer by layer, from a CAD model. This technique is credited with decentralising and democratising the production process by making it affordable and accessible.
Among several types of 3D printing technology, Stereolithography (SLA) is very popular because of its ability to produce high-accuracy, isotropic, watertight prototypes and parts.
Process outlining: SLA’s laser-based printing process involves curing/solidifying liquid photosensitive resin with ultraviolet (UV) light. The UV light works on the resin, each layer at a time, until the object is complete. Depending on the position of the light source, the build plate moves up or down as each layer solidifies.
Advantages: SLA is faster than other 3D printing technologies and is ideal for rapid 3D printing of complex geometries. Since the process is automatic, there is little human intervention. It’s also easily scalable and environment-friendly on account of low-waste generation.
Industrial applications: SLA has wide use cases in engineering, manufacturing, healthcare, education, and jewellery.
Cost factors: There are several factors influencing the cost of SLA printing, some of which are listed below.
Materials: The price of resin can vary drastically, depending on the quality, quantity and other technical parameters. Sometimes supply chain disruptions also drive up costs.
Design complexity and size: Large and complex parts take longer to print. More often than not, SLA requires support structures to securely attach a part to the print bed and prevent warping. This calls for more material. In short, compared to simple designs, intricate geometries are more resource-intensive.
Labor and post-processing: While SLA printing is inherently automatic, it still requires skilled labour – from designing a 3D model to post-processing such as sanding, polishing and other finishing touches to the final product.
Printer operating costs: Electricity usage, laser maintenance, resin tank replacement, and other upkeep contribute to operating costs.
Print volume: By increasing production, the per unit cost can be significantly reduced. A big print order can help companies achieve economies of scale as costs are spread over a large volume of goods.
Prototyping is a crucial step in product development as researchers, designers and manufacturers gain feedback from customers and other stakeholders based on an actual physical product rather than a concept. The emphasis on user needs is at the core of design thinking. The final model will be error-free, thus saving a company from resource depletion and embarrassment. With these technologies, on-demand manufacturing too has become a lot easier, saving both time and money.
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