Surface grinding is a very typical and common grinding process that is done in a CNC machine shop. It uses a rotating abrasive wheel to provide a workpiece with a smooth surface finish. The rotating abrasive wheel grinds a rough surface and eliminates irregularities to smooth it down. Often, this process is used on workpieces requiring a high surface finish or precise dimension. In addition, it can be used to remove rust or dirt from the surface of equipment before fixing it or putting it back into service.
Surface grinding is widely performed in many industries, especially in general metalworking, industrial, and job shops. If you need to know this process further, this post is exactly for you. The article will help you get all the information about surface grinding, including its definition, how it works, advantages and disadvantages, applications, some tips, etc.
What is Surface Grinding?
Surface grinding is an indispensable abrasive machining process that removes material and imparts a smooth finish to flat surfaces of parts and components. A spinning wheel, also called a grinding wheel or grit wheel, is used in the surface grinding process. This wheel is covered in rough particles to cut chips of metallic or nonmetallic substance from a workpiece, leaving a flat or smooth face.
The surface grinding process involves feeding the workpiece across a rotating abrasive wheel, which grinds the surface to the required finish specifications. The abrasive wheel spins at a high rotational speed, providing the cutting action by the grinding wheel grains as they come into contact with the workpiece. The workpiece is held and manipulated by a workholding device as it is fed across the face of the wheel, resulting in a precisely controlled finished surface.
Surface Grinding Process
Before getting into the part of how surface grinding works, let’s first understand what you need in this process. Let us take a closer look at them.
What do You Need in Surface Grinding?
Common workpiece materials cover cast iron and mild steel. While treated, these two materials are not prone to block the grinding wheel. Aluminum, stainless steel, brass, and some plastics are among the other materials. When grinding at high temperatures, the material weakens and becomes more prone to corrosion. This can also result in the loss of magnetism in applicable materials.
Component of Surface Grinder
The abrasive wheel, the workholding device, and the reciprocating or rotary table are the three essential components of a surface grinding machine. In addition, grinding dressers are an essential part.
Abrasive Wheel: The abrasive wheel is used to smooth and refine the surface of a workpiece by eliminating surplus material. Aluminum oxide, silicon carbide, diamond, and cubic boron nitride (CBN) are four frequently employed as abrasive materials on the surfaces of grinding wheels. Among these materials, aluminum oxide is the prevailing choice. Diamond and cubic boron nitride (CBN) wheels possess exceptional hardness and can economically grind materials, like ceramics and carbides, which cannot be ground using aluminum oxide or silicon.
Workholding Device: The workholding device, also known as a chuck, holds the workpiece in position when it is processed. The chuck effectively secures the material in two distinct ways: ferromagnetic pieces are securely held in position using a magnetic chuck, and non-ferromagnetic and nonmetallic pieces are secured using either vacuum or mechanical means. If only a magnetic chuck is available, a machine vise (made from ferromagnetic steel or cast iron) put on the magnetic chuck can be employed for holding non-ferromagnetic workpieces.
Table: The table moves the workpiece around and across the face of the wheel as required to obtain the desired specifications.
Grinding Dressers: Grinding dressers are employed to preserve the condition of the wheel, and they can be either mounted on a table or placed on the wheel head for convenient application.
Needs for Lubrication
Occasionally, lubricants are applied to cool the workpiece and the wheel, lubricate the interface, and remove chips. It must be put directly into the cutting area to prevent the fluid from getting carried away by the grinding wheel. Typical lubricants encompass chemical fluids, water-soluble oils, synthetic oils, and petroleum-based oils.
The types of lubricants used for grinding usually depend on the type of workpiece material:
- Aluminium: Heavy-duty oil.
- Brass: Light-duty oil.
- Cast iron: Heavy-duty emulsifiable oil; light-duty chemical and synthetic oil.
- Mild steel: Heavy-duty water-soluble oil.
- Stainless steel: Heavy-duty emulsifiable oil; heavy-duty chemical and synthetic oil.
- Plastics: Water-soluble oil; dry, heavy-duty emulsifiable oil; light-duty chemical and synthetic oil.
How does Surface Grinding Work?
Surface grinding is a finishing technique that involves using a rotating abrasive wheel to smooth the flat surface of metallic or nonmetallic materials to provide them a more refined appearance by removing the oxide layer and impurities on workpiece surfaces. This will also produce the necessary surface for functional uses.
First, the workpiece to be cut or smoothed is mounted onto a reciprocating table. In this step, a chuck is needed to keep the material in place. After the workpiece is secured to the reciprocating table, the machine slowly moves the surface of the workpiece across a grinding wheel that is spinning fast. As the grinding wheel spins, the reciprocating table carries the workpiece back and forth beneath its surface to remove surplus material until the required and even finish is obtained.
During the material removal process, excessive heat is produced, particularly when working with hard materials such as steel. This can impact the surface finish, so coolants are employed. This keeps the machining surface cool and carries the machined metallic particles away from the grinding surface to prevent surface abrasion.
Types of Surface Grinders
Typically, surface grinders are classified into three types: horizontal-spindle grinders, disc grinders and double-disc grinders, and vertical-spindle grinders.
Vertical-spindle (Wheel-face) Grinders
Vertical-spindle grinders are also known as wheel-face grinders. In this type of grinder, the face of a wheel is typically employed on a flat surface. Although a wheel-face grinder is widely utilized for quick material removal, some machines can perform high-precision work. The workpiece is secured onto a reciprocating table, which offers the flexibility to be adjusted according to the specific demands. Alternatively, it may be mounted on a rotary-table machine, allowing continuous or indexed rotation. Indexing enables loading and unloading at one station while grinding tasks are carried out at another. Typical components made using vertical-spindle grinders include stators, wafers, gears, rotors, stops and spacers, and inner rings and inner plates.
Horizontal-spindle (Peripheral) Surface Grinders
In horizontal-spindle surface grinders or peripheral surface grinders, the periphery (flat edge) of the wheel comes into contact with the workpiece to produce the flat surface. Generally, peripheral grinding works well in high-precision work on flat surfaces, tapers or angled surfaces, flat surfaces next to shoulders, and recessed surfaces. It is also suitable for slots and profiles. This type of surface grinder is utilized for grinding various components, such as pins, pistons, connecting rods, and bearing races.
Disc Grinders and Double-disc Grinders
Although disc grinding is similar to surface grinding, it has a larger contact area between the disc and the workpiece. Vertical and horizontal spindle types are both options for disc grinders. Double disc grinders can work on both sides of a workpiece at the same time. Disc grinders can achieve extremely tight tolerances. Typical components using these machines include rotors, gears, plates, spacers, and washers.
Advantages and Disadvantages of Surface Grinding
When close-tolerance dimensions and surface finishes are needed, surface grinding is often the go-to machining method. Similar to other processes, surface grinding has its advantages and disadvantages.
Advantages of Surface Grinding
Surface grinding is a cost-effective and efficient manufacturing process for high-precision surfaces. Surface grinding offers several advantages, including:
- Precise Surface Finishes: It achieves tight tolerances and smooth surface finishes by removing material in a controlled manner.
- Versatility: Surface grinding can be applied to various materials, including ferrous and non-ferrous metals, ceramics, and plastics.
- Cost-Effectiveness: Surface grinding is a cost-effective solution for achieving high-quality surface finishes compared to other methods.
- Compatibility with Automation: Surface grinding machines can be integrated into automated production lines for increased productivity.
- Increased Durability: By removing surface irregularities, surface grinding improves the durability and longevity of components.
- No Skilled Operator Required: The task is simple and may be done manually or automatically. The machine does not require a highly skilled operator when run manually.
Disadvantages of Surface Grinding
However, it’s important to consider the disadvantages of surface grinding:
- Effects on Work Material Properties: When grinding at high temperatures, the material tends to weaken and is more inclined to corrode. This can also lead to a loss of magnetism in materials where this is applicable.
- Excessive Heat Generation: The grinding process generates excessive heat during material removal, which can affect the surface finish if not properly controlled.
- Produce Abrasive Swarf: The grinding process generates the abrasive swarf that must be properly contained. It is necessary to use coolants to carry the abrasive swarf away from the grinding surface to avoid scratching the surface.
- Wear down Grinding Wheel: This process is not feasible to grind in the reverse direction. The nature of the task constantly wears down the grinding wheel and necessitates a considerable lot of spindle power.
Applications of Surface Grinding
Surface grinding is an indispensable part of machining operations in various industries. Here are some key applications of surface grinding:
Achieving Precision Flat Surfaces – Surface grinding can produce very flat surfaces with high accuracy. This makes it ideal for creating reference surfaces or precision mating surfaces. Common applications include grinding flats on gauges, bearings, valves, or machine ways.
Smoothing and Finishing – The abrasive grinding wheel can remove small imperfections and improve surface finish. Surface grinding allows it to create smooth and polished finishes.
Producing Accurate Shapes and Profiles – The grinding wheel can be dressed into different profiles to generate shapes on the workpiece. This allows the grinding of precision parts like gauges, cutting tools, mold cavities, and contoured surfaces.
Removing Stock and Squaring Blocks – Surface grinders efficiently remove material from flat surfaces and can square up blocks and flats. This makes surface grinding a useful initial rough machining process before finer precision grinding.
Cleaning up Welds and Castings – The abrasive wheel can remove burrs, weld seams, foundry defects, and flashes from castings. This provides a cleaned-up flat surface for subsequent processing.
Deburring Holes and Edges – The edge of the grinding wheel can be used to add a radius onto edges or deburr holes. This eliminates sharp edges and improves safety.
Factors Affecting Surface Grinding
Many variables influence the surface grinding process and the quality of results obtained. Here are some key factors that affect the surface grinding process:
Wheel Speed – Speed refers to the wheel RPM. Generally, the wheel RPM is usually constant in surface grinding. Note that Higher RPM allows faster material removal but can cause burn. Proper wheel speed depends on the material being ground.
Feed Rate – The traverse rate of the workpiece into the wheel. Faster feeds increase material removal rates but can cause chatter marks. Slower feeds produce finer finishes.
Depth of Cut – Deeper cuts allow more material removal per pass but can cause wheel wear, chatter, and burn marks. Lighter cuts are better for finishing operations.
Wheel Type – Depending on the hardness of the metal being ground and removed, wheels ranging from aluminum oxide and silicon carbide to diamond and CBN are used to remove material. Other specialized wheels, such as cork, are available, but these are intended for burnishing and polishing rather than material removal.
Wheel Dressing – Improper dressing can lead to glazing, rapid wheel wear, vibration, and a poor finish. The right dressing schedule maximizes cutting action.
Coolant Usage – Grinding fluids cool the workpiece and wheel, flush away chips, and prevent wheel loading. The proper type, flow rate, and filtration should be used.
Work Holding – The workpiece must be held securely to avoid chatter and aid accuracy. Proper clamping, chucks, fixtures, or magnetic/vacuum tables should be used.
Operator Skill – An experienced operator will select proper parameters and ensure quality results. Understanding the interplay of the factors is important.
Safety Precautions for Surface Grinding
Safety is paramount when engaging in surface grinding. Follow these essential precautions:
- Wear appropriate personal protective equipment (PPE), including safety glasses, face shields, gloves, and ear protection.
- Ensure the grinding machine is in good working condition and properly guarded.
- Securely fasten the workpiece using appropriate workholding devices.
- Verify that the grinding wheel is suitable for the application and securely mounted on the spindle.
- Use the correct coolant and ensure its proper application to control heat and prevent accidents.
- Regularly inspect the machine, grinding wheel, and accessories for any signs of damage or wear.
- Do not grind without proper ventilation.
- Do not strike the wheel against the material, as this action could cause faults in the wheel. More seriously, this results in a loss of integrity, and it may fly apart.
Tips for Successful Surface Grinding
To achieve optimal results in surface grinding, consider the following tips:
- Select the appropriate grinding wheel based on the workpiece material and desired finish.
- Do not grind the material for which the wheel is not designed.
- Optimize grinding parameters such as wheel speed, feed rate, and depth of cut for efficient material removal and surface quality.
- Maintain a consistent and even pressure on the workpiece to prevent uneven grinding and surface irregularities.
- Regularly dress the grinding wheel to ensure its sharpness and effectiveness.
- Monitor the grinding process closely, inspecting the surface finish periodically to make necessary adjustments.
- Keep the work area clean and free from grinding debris for safe and efficient operation.
Surface grinding is a process that involves the movement of a grinding wheel relative to the surface of the workpiece in a plane. During this process, the grinding wheel makes contact with the surface and gradually eliminates a minimal amount of material, resulting in the creation of a flat surface. Generally, the term “surface grinding” refers to any process that accurately processes or grinds a surface. The surface grinding process is often used on workpieces requiring a high surface finish or precise dimension.
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Surface grinding – From Wikipedia
There are several grinding processes available, but two of the most prevalent are surface and cylindrical grinding. The distinctions between the two processes are primarily determined by what shape you are attempting to create. Surface grinding cuts a flat, whereas cylindrical grinding cuts a round surface.
Special wheels utilizing micro-grains of cubic boron nitride (CBN) or synthetic diamond enable precision grinding of extremely hard or brittle materials.
Yes, surface grinding can be automated using computer numerical control (CNC) machines. CNC surface grinders offer enhanced precision, repeatability, and efficiency in the grinding process.