This article provides a detailed and comprehensive introduction to the technology and equipment requirements of casting post-processing. It covers various aspects such as the overview of casting post-processing, technical requirements, equipment needs, and considerations for equipment selection. Different types of cleaning methods, equipment forms, and intelligent application technologies are described. The aim is to offer guidance to foundry enterprises in the equipment selection process for casting post-processing.
Introduction
China is a major producer of castings. However, the current level of automation in post-casting cleaning is relatively low, posing as a bottleneck in the casting production process with high risks, pollution (high dust levels), and energy consumption. With the development of technology, more attention has been paid to the grinding and polishing of castings after production. However, the automation in the cutting and grinding stages of post-casting cleaning is weak and requires improvement. Many enterprises still rely on manual cleaning, which leads to various problems such as high labor intensity, labor shortage, recruitment difficulties, occupational diseases, safety hazards, high energy consumption, large dust emissions, and poor on-site working conditions. Therefore, the mechanization and automation of cutting and grinding in post-casting cleaning have become an inevitable trend.
1. Overview of Casting Post-Processing
1.1 Casting Post-Processing Categories
Casting post-processing refers to a set of rough machining systems for the finishing of castings, including shell cleaning, riser and gate cutting, casting separation, grinding, and welding. It involves equipment, logistics, and supporting intelligent auxiliary applications for the cutting, grinding of casting gates and parting lines, grinding of riser and gate root remnants, and grinding of the casting surface. The process can be divided into two production links: the pre-sequence and the post-sequence. The pre-sequence mainly includes the separation of conjoined castings, riser and gate cutting, and pre-cleaning of the parting line. Common methods include flame cutting, plasma cutting, casting separator, and carbon arc gouging, with the processing form mainly being manual cleaning, and a small amount of series manipulator form or other equipment forms. The post-sequence includes casting cutting, casting grinding, cleaning of the casting surface oxide scale, casting welding, and supporting intelligent auxiliary applications such as error correction and positioning technology, flexible technology, and system integration. Compared with the pre-sequence, the post-sequence has a larger workload, higher difficulty, and more technical challenges, and requires the addition of auxiliary intelligent functions. The cutting and grinding processes in the post-sequence can be divided into two working conditions: easy-to-achieve and difficult-to-achieve.
1.2 Technical Route Forms of Casting Post-Processing
In recent years, the grinding of castings in post-casting cleaning has received increasing attention. The grinding equipment available in the domestic and international markets mainly includes machine tool form, series (three-joint/six-joint) manipulator form, non-standard form, and hybrid structure form. The following is an elaboration on various forms of grinding equipment and supporting intelligent application technologies to help foundry enterprises select suitable grinding equipment for themselves:
(1) Machine Tool Form
Suitable for grinding small and medium-sized castings with a certain degree of complexity (such as ductile iron castings). Its motion mode is a linear axis motion method with a screw guide rail horizontal structure. The equipment volume increases correspondingly when processing larger castings. The grinding spindle is an electric spindle, and the consumable size is within a reasonable range (diamond consumables require a certain linear speed, and the larger the size, the longer the consumable life). However, the flexibility and flexibility of grinding workpieces are insufficient, and for castings that exceed a certain size, the machine tool finds it difficult to adapt to processing. During the grinding process of castings, a large amount of iron powder is generated, which penetrates into the linear motion mechanism of the machine tool along with the movement of the machine tool, causing damage to the components. Moreover, the machine tool has a large volume, and a lot of manpower will be consumed during the maintenance process. Additionally, the equipment rigidity is relatively higher than that of the series manipulator, suitable for general parting line and riser grinding, but not suitable for cutting of cast steel castings. When grinding the riser of cast steel castings, it is necessary to slow down the processing speed, resulting in relatively high energy consumption, with the main spindle power generally being more than 20 kilowatts.
(2) Series Manipulator (Three-Joint/Six-Joint) Form
Suitable for low-intensity grinding of small and medium-sized castings with a certain degree of complexity (such as ductile iron castings). Its greatest advantage is its high flexibility, suitable for logistics transportation. However, the equipment rigidity is insufficient, not suitable for riser and larger parting line grinding, requiring layered cleaning, which reduces efficiency. The end of the manipulator has a relatively small load-bearing capacity, and long-term operation will cause wear to the manipulator, reducing its lifespan (one to two years). During the grinding process of the casting, a large tangential grinding force is generated, which will act on the series manipulator, causing wear to the gears of each joint’s deceleration system, resulting in loss of accuracy and reduction in service life. Additionally, the consumable life is shortened, as a smaller-sized consumable is used, requiring a high rotational speed to compensate for the linear speed, leading to a shorter consumable life.
(3) Non-Standard Form
Designed for processing fixed workpieces, it features simple equipment, high efficiency, but a single function, which can only address certain needs of the casting and is difficult to achieve universal equipment and assembly line. It is suitable for a large number of castings with a small variety, such as stamping forms.
(4) Hybrid High-Stiffness Form
The main equipment is a new mechanism of a grinding and cutting integrated processing robot with a compact structure, strong reconfigurability, and high stiffness. It solves the problems of insufficient flexibility of traditional machine tools and low stiffness of series robots. It enables efficient grinding and cutting integration processing of different specifications of complex castings, addressing the common industry problem of “fast processing of small parts, poor processing of medium-sized parts, and inability to handle large parts”. In summary, the first three equipment forms all have varying degrees of shortcomings. The company’s independently developed hybrid high-stiffness robot can meet the requirements of cutting and grinding for various materials of small, medium, and large castings, achieving integrated grinding and cutting, and completing grinding and cutting in one sequence, achieving the benefits of saving labor, reducing logistics, lowering energy consumption, saving space, high efficiency, and a short payback period with high overall returns. The company’s products, including closed, open, and through-type models, are combined with error correction and positioning technology (such as point/line laser, contact-type automatic trajectory compensation, and spatial positioning technology), flexible technology (light stiffness flexible technology, high stiffness flexible technology), and system integration technology, and applied in practice, significantly improving the economic benefits for customers.
2. Technical Requirements and Equipment Needs of Casting Post-Processing
2.1 Technical Requirements of Casting Post-Processing
(1) Tool/Consumable Classification and Application
- Resin type: Resin slices, brown corundum grinding wheels, and zirconia corundum grinding wheels are used for casting grinding. They will be continuously consumed during the grinding process, and the grinding wheel position needs to be adjusted at any time to ensure grinding accuracy. They are often used in four-sided grinding equipment. The grinding accuracy is low, requiring a large motor power, high energy consumption, and large dust emissions.
- Diamond type: Diamond slices and diamond grinding discs are commonly used in equipment. There is no loss in cutting and grinding, and the processing accuracy is high.
- Other types: Alloy saw blades can be used for non-ferrous metal cutting and milling.
(2) Main Functional Components of Equipment
- Equipment motion power mechanism: Select a well-known brand for the screw guide rail, with warranty and after-sales service, and the structural form meets the dustproof level and dustproof design form.
- Equipment cutting and grinding functional mechanism: The spindle form is divided into electric spindle and mechanical special spindle, with different application conditions and maintenance costs. The electric spindle has high processing accuracy and low load-bearing capacity, and is suitable for the field of fine processing. When used for casting grinding, it generates a large amount of heat, and the spindle is prone to breakage, causing irreversible damage to the electric spindle. In the case of centimeter-level riser remnant conditions, the failure rate is even higher. The mechanical spindle has a low rotational speed, high stability, and high load-bearing capacity. Changes in the state of the casting’s flash and burr have a low impact on the mechanical spindle. When combined with a high-stiffness hybrid arm structure, it can quickly and effectively grind and remove centimeter-level riser remnants of the casting.
(3) Technical Requirements for Casting Cutting and Grinding
- Equipment stiffness is a necessary condition for equipment to be applied to grinding, cutting, and polishing in post-casting cleaning. Higher equipment stiffness leads to faster processing speed and higher efficiency, while lower stiffness results in lower efficiency.
- Consumable form includes the type and size of the consumable. Diamond consumables have no loss during grinding and cutting, with no dust produced by the tool. The larger the size, the lower the consumable cost, while also meeting the requirements of rough processing accuracy in post-casting cleaning.
- The consumable grinding and cutting linear speed is an important parameter in the consumable cutting and grinding process. Corresponding linear speeds are required for different types of consumables to ensure the longest possible consumable life and processing efficiency.
2.2 Equipment Requirements for Casting Post-Processing
2.2.1 Basic Requirements
(1) Easy-to-Achieve Working Conditions
For normal small and medium-sized workpieces (cast iron and non-ferrous metals), the equipment currently available on the market basically meets the grinding requirements. Customers can choose according to the characteristics of their own products, but long-term considerations should also be taken, such as whether the existing equipment can meet future needs in terms of later changes in casting products, including casting size, material, and casting process, to reduce the cost of purchasing equipment in the later stage.
(2) Difficult-to-Achieve Working Conditions
For special materials (three highs) with characteristics of high viscosity, high heat, and high hardness (including elements such as nickel, chromium, silicon, molybdenum, manganese, etc.) for small and medium-sized parts cutting and grinding, a closed equipment grinding and cutting integrated robot is selected (as shown in Figure 1).
2.2.2 Equipment Introduction
(1) Applicable to Small Cast Steel, Cast Iron, and Non-Ferrous Metal Castings
- Product features:
- High stiffness: The rigidity of the hybrid manipulator is more than 20 times that of the series manipulator.
- Spindle form: High-stiffness grinding and cutting dedicated spindle system, with fast processing speed and high accuracy.
- Flexibility: Multi-axial, with the equipment’s axial motion being five + two axes, and the auxiliary axis for hole boring.
- Tooling/fixture: Mechanical locking, firm and safe, convenient for replacement, and low cost.
- Consumable application: Stable equipment grinding, long consumable life, and low cost per piece.
- Low energy (power) consumption: The normal operating power of the equipment is 3 to 5 kilowatts.
- Intelligent configuration: Laser (point/line) detection and correction, and automatic trajectory compensation function.
- Installation and commissioning: Short on-site installation and commissioning period, and short teaching programming time.
(2) Applicable to Medium and Large Cast Steel Castings
For medium and large castings and cast steel materials with larger riser and parting lines, larger casting deviations, and high requirements for equipment stiffness and processing stroke, an open high-stiffness grinding and cutting integrated universal robot (as shown in Figure 2) is selected, with a multi-tool head form, integrated cutting and grinding in one sequence application, and the auxiliary error correction and positioning technology can effectively solve the problems of riser and gate cutting and grinding.
- Product features:
- Multi-tool combination form, completing cutting, grinding, and fine processing in one sequence, doubling the efficiency and overall cost performance by combining multiple sequences into one.
- Multi-axial (twelve motion axes), with high completion degree, and a flipping mechanism configured for the fixed mechanism (tooling).
- Exclusive design: Forms such as single, double workstations, and through-type improve efficiency.
- The equipment and turntable are designed separately, with high load-bearing capacity, solving the problem of difficult grinding for large castings due to weight limitations.
- High stiffness, with obvious structural advantages, effectively removing large riser grinding and cutting, with high efficiency, high accuracy, and low energy consumption.
- The overall floor area of a single machine and supporting production line is small, saving space and reducing logistics.
- Suitable for grinding and cutting applications of cast steel, cast iron, cast aluminum, non-ferrous metals, and precision castings.
- One person can operate multiple machines, solving the problems of labor shortage and recruitment difficulties.
- Error correction and positioning technology: Point/line laser, contact-type automatic trajectory compensation, and spatial positioning technology.
(3) Applicable to Rapidly Processed Circular Castings (Such as Brake Drums, Wheels, and Pressure Plates)
- Select a linear through-type, with an automatic loading and unloading logistics line built into the equipment for efficient and rapid grinding of castings.
- Equipment features:
- Multi-axial and flexible: X, Y, Z, A, B, W, U, V forms (A and B are grinding wheel compound axes, W axis is the workpiece rotation axis, U axis is the power head milling axis, and V is the workpiece pushing axis).
- Multi-functional integration: The top milling power head mechanism and the grinding spindle operate simultaneously, with fast processing speed, and an average processing efficiency of 6 to 8 seconds per piece.
- Man-machine efficiency ratio: 4 to 8:1, universal for grinding and cutting, and integrated grinding and cutting.
(4) Grinding of riser and oxide scale cleaning for other large castings
- High-stiffness flexible grinding technology: Mainly used to solve the problems of riser root remnants, sand adhesion, and excessive meat on large castings. The auxiliary shaft floating mechanism is suitable for grinding a series of holes in the castings, and the mechanical spindle floating mechanism is suitable for grinding planar and arc surfaces. Combined with spatial origin positioning technology, force feedback mechanism, force control remote control technology, teaching programming, automatic trajectory compensation, and laser point and line detection.
- Low-stiffness flexible grinding technology: Mainly applied to series manipulator equipment, with radial floating mechanism and axial floating mechanism, mainly used for cleaning the surface position of the castings, such as grinding of wind turbine blade castings, hole position grinding, and cleaning of the inner surface of the castings, such as grinding of machine tool castings.
(5) Supporting Intelligent Application Technology
- Error correction and positioning technology:
- Contact-type automatic trajectory compensation technology: A contact-type detection form with low cost, light weight, easy installation, and simple control program. It is suitable for working in a high dust environment, without being affected by dust, with high detection accuracy, and not being affected by the concave and convex features of the casting surface.
- Point laser detection technology: Advantages include relatively low cost and simple operation; disadvantages include low data collection efficiency and poor data collection accuracy.
- Line laser detection technology: High data collection efficiency, high accuracy, relatively high cost, complex operation, and high requirements for personnel.
- Spatial positioning technology: The force control remote operation technology combined with the spatial origin positioning technology provides the best accuracy and operational convenience. The force control remote operation is to drive the high-stiffness equipment or the slave unit of the series manipulator by the active control unit to complete the grinding work.
- Flexible technology includes high-stiffness flexible technology and light-stiffness flexible technology:
- High-stiffness flexible technology is another form of high-stiffness flexible grinding technology developed by Tianjin Zhongyiming Technology Co., Ltd. in combination with the high-stiffness characteristics of the hybrid structure. It is applied to the working conditions of large grinding amount removal on the casting surface, including the remnants after fire cutting, riser root remnants, excessive meat, and sand adhesion, significantly improving the processing efficiency.
- Light-stiffness flexible technology is mainly used for the surface treatment of castings and is not suitable for high-intensity grinding. In the case of working conditions such as excessive meat and riser remnants on the casting surface, the efficiency of light-stiffness flexible grinding is low, the equipment load is too high, and the service life of the equipment is reduced.
(6) Equipment, Logistics, and Supporting Intelligent Integrated Application
- Method 1: Combine the main grinding equipment with the manipulator and configure the detection function to form an automated production line form.
- Method 2: Combine the main grinding equipment with the truss manipulator and match it with the logistics line for an automated grinding production line form, suitable for the integrated application of cutting and grinding for small and medium-sized castings.
- Through-type automated production line form: Only need to connect with the incoming material line to solve the grinding of circular castings, connecting the production line with the post-cleaning line, saving many intermediate links, improving efficiency, increasing production capacity, and reducing operating costs.
- Open automated production line form: The multi-tool head function simplifies multiple processes into one sequence, processes medium and large castings with the conveyor line, and uses the detection technology to solve the casting deviation to ensure processing accuracy, such as the application of large cylinder block production systems, the integrated application of grinding and cutting for railway system bolster products, and the integrated application of grinding and cutting for bridge shell castings.
2.3 Considerations for Equipment Selection in Casting Post-Processing
- Sample testing: The actual testing effect and efficiency of the sample can reflect the actual application ability of the equipment.
- Equipment parameters and process parameters: Grinding speed, equipment load, equipment energy consumption, dust removal and dustproof, etc.
- Universality and flexibility: It can cover a variety of products, with high grinding completion, reducing processes and investment.
- Programming efficiency: Equipment with a rapid programming ability due to its core algorithm, otherwise, it is low.
- Applicable materials: The grinding and cutting equipment should be adaptable to various workpiece materials, such as heat-resistant steel, high-nickel steel, cast steel, cast iron, non-ferrous metals, etc.
- Equipment processing accuracy and surface quality.
- Configuration of equipment functional components and dustproof performance of the equipment.
