Thermoplastic Materials - ABS (Acrylonitrile/ Butadiene/ Styrene)

Rapid prototype made with ABS thermoplastic materials

ABS is a strong, durable production-grade thermoplastic used across many industries.

ABS is an ideal material for conceptual prototyping through design verification through direct digital manufacturing. The marriage of ABS with FDM (Fused Deposition Modeling) technology gives you the ability to create Real Parts™ direct from digital files, in a variety of standard and custom colors. This material is ideal for the rapid production of prototypes, tooling and the direct (tool-less) manufacturing of production parts.

ABS is widely used in applications where impact-resistance and structural strength are necessary. It is accurate, durable and robust enough for field testing or demonstration units. Because of its excellent dimensional stability, it is ideal for pre-production rapid prototypes that can accurately predict performance of injection molded parts.

ABS is ideal for any of the following applications:

concept modeling
Form, fit , function
Design verification
master for RTV molding and vacuum forming

· · Jigs and fixtures

· · Marketing tools

· · Thermoforming

FDM Thermoplastics

The Difference is in Our Materials

Choose from a wide variety of high-performance engineering materials for your detailed functional prototypes, durable manufacturing tools and low-volume manufacturing needs.

While competitors simulate thermoplastics using powders and resins, parts produced using RedEye's FDM technologies are made with real production-grade thermoplastics. The same raw materials used in the gold standard of manufacturing - injection molding.

FDM Material Options

	ABS - (Acrylonitrile/butadiene/styrene) Durable engineering grade plastic.
	ABSi - (ABS with high impact strength) The extra durability of this engineering grade plastic has higher impact strength than normal ABS. Its appearance is semi-translucent.

ABS Plastics (Acrylonitrile - Butadiene - Styrene)

ABS plastic is an easily machined, tough, low cost rigid thermoplastic plastic with high impact strength, ideal for turning, drilling, milling, sawing, die-cutting, shearing.
ABS plastics are composed of acrylonitrile, butadiene, and styrene in varying proportions, combined by a variety of methods including graft copolymerization and physical blending. Originally an outgrowth of polystyrene modification, the plastics long have been in a category of their own. ABS plastics provide a balanced combination of mechanical toughness, wide temperature range, good dimensional stability, chemical resistance, electrical insulating properties, and ease of fabrication. ABS plastics are produced in a wide range of grades including medium and high-impact, heat-resistant, plateable fire-retardant, and both low and high gloss varieties. ABS plastics are available as compounds for injection molding, blow molding, extrusion, and calendaring, as sheet for thermoforming or cold forming, and in expandable grades for foam molding.
Applications. ABS applications are extremely broad, falling between commodity plastics and the engineering resins. ABS fills the property re1quirement for many parts at a reasonable price.

'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.^[1]^[2] Construction of the part or assembly is usually done using 3D printing or "additive layer manufacturing" technology.^[3]
The first methods for rapid prototyping became available in the late 1980s and were used to produce models and prototype parts. Today, they are used for a wide range of applications^[4] and are used to manufacture production-quality parts in relatively small numbers if desired without the typical unfavorable short-run economics. This economy has encouraged online service bureaus. Historical surveys of RP technology^[2] start with discussions of simulacra production techniques used by 19th-century sculptors. Some modern sculptors use the progeny technology to produce exhibitions.^[5] The ability to reproduce designs from a dataset has given rise to issues of rights, as it is now possible to interpolate volumetric data from one dimensional images.
As with CNC subtractive methods, the computer-aided-design - computer-aided manufacturing CAD-CAM workflow in the traditional Rapid Prototyping process starts with the creation of geometric data, either as a 3D solid using a CAD workstation, or 2D slices using a scanning device. For RP this data must represent a valid geometric model; namely, one whose boundary surfaces enclose a finite volume, contain no holes exposing the interior,and do not fold back on themselves. In other words, the object must have an “inside.” The model is valid if for each point in 3D space the computer can determine uniquely whether that point lies inside, on, or outside the boundary surface of the model. CAD post-processors will approximate the application vendors’ internal CAD geometric forms (e.g., B-splines) with a simplified mathematical form, which in turn is expressed in a specified data format which is a common feature in Additive Manufacturing: STL (stereolithography) a de facto standard for transferring solid geometric models to SFF machines. To obtain the necessary motion control trajectories to drive the actual SFF, Rapid Prototyping, 3D Printing or Additive Manufacturing mechanism, the prepared geometric model is typically sliced into layers, and the slices are scanned into lines [producing a "2D drawing" used to generate trajectory as in CNC`s toolpath], mimicking in reverse the layer-to-layer physical building process.[2]
Fused deposition modeling (FDM) is an additive manufacturing technology commonly used for modeling, prototyping, and production applications.
FDM works on an "additive" principle by laying down material in layers; a plastic filament or metal wire is unwound from a coil and supplies material to produce a part.
The technology was developed by S. Scott Crump in the late 1980s and was commercialized in 1990.^[1]
The term fused deposition modeling and its abbreviation to FDM are trademarked by Stratasys Inc. The exactly equivalent term, fused filament fabrication (FFF), was coined by the members of the RepRap project to give a phrase that would be legally unconstrained in its use.

History

http://upload.wikimedia.org/wikipedia/commons/thumb/4/42/FDM_by_Zureks.png/220px-FDM_by_Zureks.png

Fused deposition modeling: 1 – nozzle ejecting molten plastic, 2 – deposited material (modeled part), 3 – controlled movable table.

Main article: Fused deposition modeling

Fused deposition modeling (FDM) was developed by S. Scott Crump in the late 1980s and was commercialized in 1990 by Stratasys.^[2] With the expiration of the patent on this technology there is now a large open-source development community, as well as commercial and DIY variants, which utilize this type of 3D printer. This has led to a two orders of magnitude price drop since this technology's creation.

Process

FDM begins with a software process which processes an STL file (stereolithography file format), mathematically slicing and orienting the model for the build process. If required, support structures may be generated. The machine may dispense multiple materials to achieve different goals: For example, one may use one material to build up the model and use another as a soluble support structure,^[3] or one could use multiple colors of the same type of thermoplastic on the same model.
The model or part is produced by extruding small beads of thermoplastic material to form layers as the material hardens immediately after extrusion from the nozzle.
A plastic filament or metal wire is unwound from a coil and supplies material to an extrusion nozzle which can turn the flow on and off. There is typically a worm-drive that pushes the filament into the nozzle at a controlled rate.
The nozzle is heated to melt the material. The thermoplastics are heated past their glass transition temperature and are then deposited by an extrusion head.
The nozzle can be moved in both horizontal and vertical directions by a numerically controlled mechanism. The nozzle follows a tool-path controlled by a computer-aided manufacturing (CAM) software package, and the part is built from the bottom up, one layer at a time. Stepper motors or servo motors are typically employed to move the extrusion head. The mechanism used is often an X-Y-Z rectilinear design, although other mechanical designs such as deltabot have been employed.
Although as a printing technology FDM is very flexible, and it is capable of dealing with small overhangs by the support from lower layers, FDM generally has some restrictions on the slope of the overhang, and cannot produce unsupported stalactites.
Myriad materials are available, such as ABS, PLA, polycarbonate, polyamides, polystyrene, lignin, among many others, with different trade-offs between strength and temperature properties.

FDM, a prominent form of rapid prototyping, is used for prototyping and rapid manufacturing. Rapid prototyping facilitates iterative testing, and for very short runs, rapid manufacturing can be a relatively inexpensive alternative.^[4]
FDM uses the thermoplastics ABS, ABSi, polyphenylsulfone (PPSF), polycarbonate (PC), and Ultem 9085, among others. These materials are used for their heat resistance properties. Ultem 9085 also exhibits fire retardancy making it suitable for aerospace and aviation applications.
FDM is also used in prototyping scaffolds for medical tissue engineering applications.^[5]

Three point flexural test

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http://upload.wikimedia.org/wikipedia/commons/thumb/6/60/Trois-points-p1040189.jpg/220px-Trois-points-p1040189.jpg

1940s flexural test machinery working on a sample of concrete

http://upload.wikimedia.org/wikipedia/commons/thumb/d/d9/Three_point_flexural_test.jpg/220px-Three_point_flexural_test.jpg

Test fixture on universal testing machine for three point flex test

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The three point bending flexural test provides values for the modulus of elasticity in bending

, flexural stress $\sigma_f$ , flexural strain $\epsilon_f$ and the flexural stress-strain response of the material. The main advantage of a three point flexural test is the ease of the specimen preparation and testing. However, this method has also some disadvantages: the results of the testing method are sensitive to specimen and loading geometry and strain rate.

Testing method

The test method for conducting the test usually involves a specified test fixture on a universal testing machine. Details of the test preparation, conditioning, and conduct affect the test results.
Calculation of the flexural stress $\sigma_f$

$\sigma_f = \frac{3 F L}{2 b d^2}$ for a rectangular cross section

$\sigma_f = \frac{F L}{\pi R^3}$ for a circular cross section^[1]

Calculation of the flexural strain $\epsilon_f$

$\epsilon_f = \frac{6Dd}{L^2}$

Calculation of flexural modulus

^[2]

$E_f = \frac{L^3 m}{4 b d^3}$

in these formulas the following parameters are used:

$\sigma_f$ = Stress in outer fibers at midpoint, (MPa)
$\epsilon_f$ = Strain in the outer surface, (mm/mm)
= flexural Modulus of elasticity,(MPa)
= load at a given point on the load deflection curve, (N)
= Support span, (mm)
= Width of test beam, (mm)
= Depth of tested beam, (mm)
= maximum deflection of the center of the beam, (mm)
= The gradient (i.e., slope) of the initial straight-line portion of the load deflection

curve,(P/D), (N/mm)

= The radius of the beam, (mm)

Fracture toughness testing

http://upload.wikimedia.org/wikipedia/commons/thumb/0/0c/SingleEdgeNotchBending.svg/300px-SingleEdgeNotchBending.svg.png

Single edge notch bending specimen (also called three point bending specimen) for fracture toughness testing.

The fracture toughness of a specimen can also be determined using a three-point flexural test. The stress intensity factor at the crack tip of a single edge notch bending specimen is^[3]

$\begin{align} K_{\rm I} & = \frac{4P}{B}\sqrt{\frac{\pi}{W}}\left[1.6\left(\frac{a}{W}\right)^{1/2} - 2.6\left(\frac{a}{W}\right)^{3/2} + 12.3\left(\frac{a}{W}\right)^{5/2} \right.\\ & \qquad \left.- 21.2\left(\frac{a}{W}\right)^{7/2} + 21.8\left(\frac{a}{W}\right)^{9/2} \right] \end{align}$

where

is the applied load,

is the thickness of the specimen,

is the crack length, and

is the width of the specimen. In a three-point bend test, a fatigue crack is created at the tip of the notch by cyclic loading. The length of the crack is measured. The specimen is then loaded monotonically. A plot of the load versus the crack opening displacement is used to determine the load at which the crack starts growing. This load is substituted into the above formula to find the fracture toughness $K_{Ic}$ .
The ASTM E1290-08 Standard suggests the relation

$K_{\rm I}= \cfrac{6P}{BW}\,a^{1/2}\,Y$

where

$Y=\cfrac{1.99-a/W\,(1-a/W)(2.15-3.93a/W+2.7(a/W)^{2})}{(1+2a/W)(1-a/W)^{3/2}} \,.$

The predicted values of $K_{\rm I}$ are nearly identical for the ASTM and Bower equations for crack lengths less than 0.6

Standards

ISO 12135: Metallic materials. Unified method for the determination of quasi-static fracture toughness
ISO 12737: Metallic materials. Determination of plane-strain fracture toughness
ASTM D790: Standard test methods for flexural properties of unreinforced and reinforced plastics and electrical insulating materials
ISO 178: Plastics—Determination of flexural properties
ASTM E1290: Standard Test Method for Crack-Tip Opening Displacement (CTOD) Fracture Toughness Measurement.

Flexural Properties Testing

Testing the flexural properties of Plastics and Polymers by using ASTM D790 and ISO 178

Flexural Properties Testing Scope:
The flexural test measures the force required to bend a beam under three point loading conditions. The data is often used to select materials for parts that will support loads without flexing. Flexural modulus is used as an indication of a material’s stiffness when flexed. Since the physical properties of many materials (especially thermoplastics) can vary depending on ambient temperature, it is sometimes appropriate to test materials at temperatures that simulate the intended end use environment.

Flexural Test Procedure:
Most commonly the specimen lies on a support span and the load is applied to the center by the loading nose producing three point bending at a specified rate. The parameters for this test are the support span, the speed of the loading, and the maximum deflection for the test. These parameters are based on the test specimen thickness and are defined differently by ASTM and ISO. For ASTM D790, the test is stopped when the specimen reaches 5% deflection or the specimen breaks before 5%. For ISO 178, the test is stopped when the specimen breaks. If the specimen does not break, the test is continued as far a possible and the stress at 3.5% (conventional deflection) is reported.
Elevated or Reduced Temperature Test Procedure:
A thermal chamber is installed on the universal test machine. The chamber is designed to allow the test mounts from the base and crosshead of the universal tester to pass through the top and bottom of the chamber. Standard test fixtures are installed inside the chamber, and testing is conducted inside the controlled thermal environment, the same as it would be at ambient temperature. The chamber has internal electric heaters for elevated temperatures, using external carbon dioxide gas as a coolant for reduced temperatures.

Specimen size:
A variety of specimen shapes can be used for this test, but the most commonly used specimen size for ASTM is 3.2mm x 12.7mm x 125mm (0.125" x 0.5" x 5.0") and for ISO is 10mm x 4mm x 80mm.

Data:
Flexural stress at yield, flexural strain at yield, flexural stress at break, flexural strain at break, flexural stress at 3.5% (ISO) or 5.0% (ASTM) deflection, flexural modulus. Stress/Strain curves and raw data can be provided.

*ASTM and ISO specify somewhat different parameters for this test.
**Please note that this test description is intentionally generic in nature and aimed at providing a descriptive summary to enhance test understanding. Standards can be obtained from appropriate standards authorities.

Flexural plastics testing:

Impact Testing

Impact testing is testing an object's ability to resist high-rate loading. An impact test is a test for determining the energy absorbed in fracturing a test piece at high velocity. Most of us think of it as one object striking another object at a relatively high speed.

Why is Impact Testing Important?

Impact resistance is one of the most important properties for a part designer to consider, and without question, the most difficult to quantify. The impact resistance of a part is, in many applications, a critical measure of service life. More importantly these days, it involves the perplexing problem of product safety and liability.

One must determine:

the impact energies the part can be expected to see in its lifetime,
the type of impact that will deliver that energy, and then
select a material that will resist such assaults over the projected life span.

Molded-in stresses, polymer orientation, weak spots (e.g. weld lines or gate areas), and part geometry will affect impact performance. Impact properties also change when additives, e.g

coloring agents, are added to plastics.

Ductile vs. Brittle

Most real world impacts are biaxial rather than unidirectional.
Further complication is offered by the choice of failure modes: ductile or brittle. Brittle materials take little energy to start a crack, little more to propagate it to a shattering climax. Other materials possess ductility to varying degrees. Highly ductile materials fail by puncture in drop weight testing and require a high energy load to initiate and propagate the crack.

Many materials are capable of either ductile or brittle failure, depending upon the type of test and rate and temperature conditions. They possess a ductile/brittle transition that actually shifts according to these variables.

ABS materials

Tuesday, January 28, 2014