Freeform surface machining

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FREE-FORM SURFACE MILLING

Freeform surface or complex surfaces are widely manufactured nowadays. The industries which most often manufactures free-form surfaces are basically aerospace, automotive, die mold industries, bio medical and power sector for turbine blades manufacturing. Generally 3 or 5 axis CNC milling machine is used for this purpose. The manufacturing process of free form surface is not an easy job as the tool path generation in present CAM technology is generally based on geometric computation so tool path are not optimum. The geometry can also be not described explicitly so errors and discontinuities occurrence in the solid structure cannot be avoided. Free-form surfaces are machined with the help of different tool path generation method like adaptive iso-planar tool path generation, constant scallop tool path generation, adaptive iso-parametric method, iso-curvature, isophote and by other methods. The different methods are chosen based on the parameters which is needed to be optimized. [1] [2]

Aerospace engineering effort to fly in the atmosphere of Earth (aeronautics) and surrounding space (astronautics)

Aerospace is the human effort in science, engineering, and business to fly in the atmosphere of Earth (aeronautics) and surrounding space (astronautics). Aerospace organizations research, design, manufacture, operate, or maintain aircraft or spacecraft. Aerospace activity is very diverse, with a multitude of commercial, industrial and military applications.

Turbine rotary mechanical device that extracts energy from a fluid flow

A turbine is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating electrical power when combined with a generator. A turbine is a turbomachine with at least one moving part called a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades so that they move and impart rotational energy to the rotor. Early turbine examples are windmills and waterwheels.

Computer-aided manufacturing use of computer software to control machine tools

Computer-aided manufacturing (CAM) is the use of software to control machine tools and related ones in the manufacturing of workpieces. This is not the only definition for CAM, but it is the most common; CAM may also refer to the use of a computer to assist in all operations of a manufacturing plant, including planning, management, transportation and storage. Its primary purpose is to create a faster production process and components and tooling with more precise dimensions and material consistency, which in some cases, uses only the required amount of raw material, while simultaneously reducing energy consumption. CAM is now a system used in schools and lower educational purposes. CAM is a subsequent computer-aided process after computer-aided design (CAD) and sometimes computer-aided engineering (CAE), as the model generated in CAD and verified in CAE can be input into CAM software, which then controls the machine tool. CAM is used in many schools alongside Computer-Aided Design (CAD) to create objects.

Contents

Different tool path generation methods

  1. Iso-planar tool path method: This is the most common and robust method used to machine free-form surface. In this process tool path generation is done by intersection of surfaces with parallel plane in Cartesian space.
  2. Adaptive iso-planar tool path method: In this process the surface are partitioned into different regions according to their slope with the intersection planes by applying the concept of isophote.
  3. Iso-scallop method: Scallop generated between two adjacent machining path is constant. [3] [4]

Optimization of free-form surface machining

CAM software generally creates a tool path without considering any mechanics process. These causes risk of tool damage, tool deflection and errors on surface finish. By minimizing the forces we can increase tool life. Different optimization method can be used considering process parameters like feed rate, spindle speed, steps, tool diameter, magnitude and preset maximum force. The optimization can be done for minimum machining time, minimum tool travel, minimum production cost or for good surface finish. Efficiency of surface machined is also considered by maximum scallop height and by gouging. Gouging are the main reason for discrepancies of surface accuracy and texture specification. It also causes damage to part,s surface and machine tool. Scallop height tolerance help us in measuring the quality of free-form surface. Selection of proper topology result in minimum path length. In CAM software choosing NURBS to create surface is considered to be good method for presenting surface as it is accepted by both IGES and STEP files of CAM software. [5]

IGES file format

The Initial Graphics Exchange Specification (IGES) is a vendor-neutral file format that allows the digital exchange of information among computer-aided design (CAD) systems.

See also

Freeform surface modelling

Freeform surface modelling is a technique for engineering freeform surfaces with a CAD or CAID system.

G-code, which has many variants, is the common name for the most widely used numerical control (NC) programming language. It is used mainly in computer-aided manufacturing to control automated machine tools.

Multiaxis machining

Multiaxis machining is a manufacturing process that involves tools that move in 4 or more directions and are used to manufacture parts out of metal or other materials by milling away excess material, by water jet cutting or by laser cutting. This type of machining was originally performed mechanically on large complex machines. These machines operated on 4,5,6,and even 12 axes which were controlled individually via levers that rested on cam plates. The cam plates offered the ability to control the tooling device, the table in which the part is secured to, as well as rotating the tooling or part within the machine. Due to the machines size and complexity it took extensive amounts of time to set them up for production. Once computer numerically controlled machining was introduced it provided a faster, more efficient method for machining complex parts. Typical CNC tools support translation in 3 axis; multiaxis machines also support rotation around one or multiple axis. 5-axis machines are commonly used in industry in which the workpiece is translated linearly along three axes and the tooling spindle is capable of rotation about 2 additional axes.

Related Research Articles

Computer-aided design constructing a product by means of computer

Computer-aided design (CAD) is the use of computers to aid in the creation, modification, analysis, or optimization of a design. CAD software is used to increase the productivity of the designer, improve the quality of design, improve communications through documentation, and to create a database for manufacturing. CAD output is often in the form of electronic files for print, machining, or other manufacturing operations. The term CADD is also used.

Mastercam is a suite of Computer-Aided Manufacturing (CAM) and CAD/CAM software applications. Founded in MA in 1983, CNC Software, Inc. is one of the oldest developers of PC-based computer-aided design / computer-aided manufacturing (CAD/CAM) software. They are one of the first to introduce CAD/CAM software designed for both machinists and engineers. Mastercam, CNC Software’s main product, started as a 2D CAM system with CAD tools that let machinists design virtual parts on a computer screen and also guided computer numerical controlled (CNC) machine tools in the manufacture of parts. Since then, Mastercam has grown into the most widely used CAD/CAM package in the world. CNC Software, Inc. is now located in Tolland, Connecticut.

Creo Elements/Pro, formerly known as Pro/ENGINEER and Wildfire, is a 3D CAD, CAM, CAE, and associative solid modelling app. It is one of a suite of 10 collaborative applications that provide solid modelling, assembly modelling, 2D orthographic views, finite element analysis, direct and parametric modelling, sub-divisional and NURBS surface modelling, and NC and tooling functionality for mechanical designers. Creo Elements/Parametric compete directly with Solidworks, CATIA, and NX/Solid Edge. It was created by Parametric Technology Corporation (PTC) and was the first of its kind to market.

CAD data exchange is a modality of data exchange used to translate data between different Computer-aided design (CAD) authoring systems or between CAD and other downstream CAx systems.

Manufacturing process management (MPM) is a collection of technologies and methods used to define how products are to be manufactured. MPM differs from ERP/MRP which is used to plan the ordering of materials and other resources, set manufacturing schedules, and compile cost data.

Rhinoceros 3D 3D computer graphics software

Rhinoceros is a commercial 3D computer graphics and computer-aided design (CAD) application software developed by Robert McNeel & Associates, an American, privately held, employee-owned company founded in 1980. Rhinoceros geometry is based on the NURBS mathematical model, which focuses on producing mathematically precise representation of curves and freeform surfaces in computer graphics.

Incremental sheet forming is a sheet metal forming technique where a sheet is formed into the final workpiece by a series of small incremental deformations. However, studies have shown that it can be applied to polymer and composite sheets too. Generally, the sheet is formed by a round tipped tool, typically 5 to 20mm in diameter. The tool, which can be attached to a CNC machine, a robot arm or similar, indents into the sheet by about 1 mm and follows a contour for the desired part. It then indents further and draws the next contour for the part into the sheet and continues to do this until the full part is formed. ISF can be divided into variants depending on the number of contact points between tool, sheet and die. The term Single Point Incremental Forming (SPIF) is used when the opposite side of the sheet is supported by a faceplate and Two Point Incremental Forming (TPIF) when a full or partial die supports the sheet.

Rapid prototyping group of techniques to quickly construct physical objects

Rapid prototyping is a group of techniques used to quickly fabricate a scale model of a physical part or assembly using three-dimensional computer aided design (CAD) data. Construction of the part or assembly is usually done using 3D printing or "additive layer manufacturing" technology.

The term "feature" implies different meanings in different engineering disciplines. This has resulted in many ambiguous definitions for feature. A feature, in computer-aided design (CAD), usually refers to a region of a part with some interesting geometric or topological properties. These are more precisely called form features. Form features contain both shape information and parametric information of a region of interest. They are now ubiquitous in most current CAD software, where they are used as the primary means of creating 3D geometric models. Examples of form features are extruded boss, loft, etc. Form feature is not the only type of feature that is discussed in CAD literature. Sometimes a part's functional or manufacturing features of the subject of attention. Although it is quite possible to see form features and manufacturing features are called by the same name, they are not exactly the same concepts. For example, one may either use the name "pocket" to refer to a swept cut on the boundary of a part model, or to refer to a trace left on the part boundary by a specific machining operation. The former is exclusively concerned with a geometric shape whereas the latter is concerned with both the geometric shape and a manufacturing operation, needing more parameters in its definition. As such, a manufacturing feature can be minimally defined as a form feature, but not necessarily vice versa. Machining features are an important subset of manufacturing features. A machining feature can be regarded as the volume swept by a "cutting" tool, which is always a negative (subtracted) volume. Finally, there is also the concept of assembly feature, which encodes the assembly method between connected components.

STEP-NC

STEP-NC is a machine tool control language that extends the ISO 10303 STEP standards with the machining model in ISO 14649, adding geometric dimension and tolerance data for inspection, and the STEP PDM model for integration into the wider enterprise. The combined result has been standardized as ISO 10303-238.

BobCAD-CAM is a developer of CAD/CAM software for the CNC metalworking and manufacturing industry. Based in Clearwater, FL, BobCAD-CAM has a staff of approximately 85 employees. Since opening in 1985 they've developed a reputation in the industry as having one of the most powerful and affordable CAD-CAM software available.

Electron-beam freeform fabrication

Electron-beam freeform fabrication (EBF3) is an additive manufacturing process that builds near-net-shape parts requiring less raw material and finish machining than traditional manufacturing methods. It uses a focused electron beam in a vacuum environment to create a molten pool on a metallic substrate.

WorkNC

WorkNC is a Computer aided manufacturing (CAM) software developed by Sescoi for multi-axis machining.

Milling (machining) machining process

Milling is the process of machining using rotary cutters to remove material by advancing a cutter into a workpiece. This may be done varying direction on one or several axes, cutter head speed, and pressure. Milling covers a wide variety of different operations and machines, on scales from small individual parts to large, heavy-duty gang milling operations. It is one of the most commonly used processes for machining custom parts to precise tolerances.

CNC plunge milling

CNC plunge milling, also called z-axis milling, is a CNC milling process. In this process, the feed is provided linearly along the tool axis while doing CNC processing.

Virtual machining is the practice of using computers to simulate and model the use of machine tools for part manufacturing. Such activity replicates the behavior and errors of a real environment in virtual reality systems. This can provide useful ways to manufacture products without physical testing on the shop floor. As a result, time and cost of part production can be decreased.

Design for additive manufacturing is design for manufacturability as applied to additive manufacturing (AM). It is a general type of design methods or tools whereby functional performance and/or other key product life-cycle considerations such as manufacturability, reliability, and cost can be optimized subjected to the capabilities of additive manufacturing technologies.

NCSIMUL

NCSIMUL is a software program developed by the company SPRING Technologies, that is used for simulating, verifying, and optimizing CNC machining in a 3-step process. It reads the post-processed G-code to identify the tool path, and replicates the material removal process of the machine by cutting volumes. It then identifies all syntax errors in the code, crashes in the machining environment, and deviations from the modeled CAD part.

References

  1. ↑ Lazoglu, I (2009). "Tool path optimization for free form surface machining". CIRP Annals - Manufacturing Technology. 58 (2009): 101–104. doi:10.1016/j.cirp.2009.03.054.
  2. ↑ Ding, S (February 2003). "Adaptive iso-planar tool path generation for machining of free-form surfaces". Computer-Aided Design. 35 (2): 141–153. doi:10.1016/s0010-4485(02)00048-9.
  3. ↑ Kumar, Rajneesh (2006). "Optimization of CNC iso-scallop free form surface machining using a genetic algorithm". International Journal of Machine Tools and Manufacture. 46 (7–8): 811–819. doi:10.1016/j.ijmachtools.2005.07.028.
  4. ↑ Lasemi, Ali (2010). "Recent development in CNC machining of freeform surfaces: A state-of-the-art review". Computer-Aided Design. 42 (7): 641–654. doi:10.1016/j.cad.2010.04.002.
  5. ↑ Poniatowska, Malgorzata (2015). "Free-form surface machining error compensation applying 3D CAD machining pattern model". Computer-Aided Design. 62: 227–235. doi:10.1016/j.cad.2014.12.003.
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