Introduction to the Universal Testing Machine
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Universal Testing Machines (UTMs) are also commonly referred to as tensile testers, pull testers, or materials testing systems. UTMs are at the heart of material science and play a critical role in almost every manufacturing environment. The annual global market for these types of machines is $500 million which includes machines, accessories, software, and services(MRO). This article will go into detail about the history of universal testing machines, how they work, and how to specify the right testing system for your specific ASTM procedure or application.
Universal Testing Machines have existed in various forms since the 1800’s. One of the original applications was for testing the strength of steel used in steam power boilers. These boilers would encapsulate large amounts of steam pressure, and explosions were both catastrophic and fairly common. One of the largest explosions occurred in Manhattan in 1850 at a machine shop on what is now Pearl St. and killed over 60 people.
The History Of Galdabini and Tensile Testers in Italy:
Galdabini (est. 1890) entered the market in the early 1900s with a series of dead-weight testing machines and developed their own universal testing machine in 1934. During this time Galdabini also developed some of the largest metal straightening machines and hydraulic presses in the world. The company is the 2nd oldest continuously operating manufacturer of these types of UTM materials testing systems.
The picture above shows the historical Galdabini manufacturing plant during the second world war in the 1940's. The company was founded by Emilia Crespi and Cesare Galdabini in Gallarate, Italy which is near Milan in the northern part of the country. The town of Gallarate was vital to Italy's textile industry during the early 1900's. The Galdabini factory originally supported this textile manufacturing and quickly expanded into building machine tools such as hydraulic stamping machines and metal tube bending machines.
Working Principle of UTMs:
Today's Universal Testing Machines use a rotating ball screw in order to drive a load-bearing crosshead up and down. An electrical motor powers a series of pulleys and gears which turn the screw, creating the crosshead motion. The motion of the electrical motor is controlled using pulse width modulation (PWM) by an astable oscillator circuit. Tensile testers are relatively robust in design and therefore have a small amount of failure modes. Therefore universal testing machines need relatively little maintenance and are easy to fix in the event of a break down.
Aside from the machine, a few other components are required to make up the complete system. A load cell is used to measure the force during the test. A position sensor, most commonly an encoder, is used to measure the location of the crosshead. Most machines are controlled using the position data channel, and will move at a software controlled rate of speed according to the desired ASTM test or similar procedure.
Types of Universal Testing Machines:
There are several types of UTMs which exist under the larger umbrella of material testing systems. For our purposes, we will focus only on static, axial-loading, tension/compression type machines. Other types of testing machines which will not be discussed here include electro-dynamic testers, impact testers, servo-hydraulic fatigue systems, torsion testers, torsional bi-axial machines, and planar bi-axial machines.
Single Column Machines
Single column Universal testing machines, also uncommonly known as C-frame testers because of their shape, have the smallest footprint and capacity. These systems are typically used on a benchtop and their loading capacities can range from several ounces to about 1,000 lbs. Virtually every single column machine is electromechanical and uses a small servo-electric motor for both power and control. Have a testing application that requires more than 1,000 lbs.? You will need to use a dual column machine or else risk bending the machine.
Dual Column Machines
A dual column test stand is also referred to as an H frame because of its design. The H frame construction is extremely robust and was the basis for some of the very first universal testing machines. These systems can range in capacity from 500 to over 100,000 lbs. The largest Universal Testing Machine ever manufactured is housed at the National Institute of Standards and Technology (NIST) in Gaithersburg MD. The machine is over 100 ft. high and is capable of applying forces up to 12,000,000 lbs. This machine is driven by a hydraulic system.
Dual Column UTM’s can be either electromechanical or servo-hydraulic. Generally, hydraulic machines are better suited for extremely repetitive testing of high strength materials in production environments. The electro-mechanical machines are much more versatile in terms of their speed, and length of stroke, which better suits them for R&D environments where many different types of tests can be performed. The electro-mechanical ballscrew testing machines are also much easier to transport and ship.
Specifying the right Machine, Controller, LC + Grip
There are four major steps involved when specifying a Universal Testing Machine. While these machines are considered to be “universal” it still takes a considerable amount of foresight and planning in order to get the perfect machine for your lab.
1. Selecting the Right Test Frame
The test frame is the most critical component of the system because it determines the base capacity of the entire setup. The test frame is not necessarily upgradeable, so proper care must be taken to select enough capacity. The machine capacity is reliant on the application. The larger machines can fulfill a wide range of test procedures however they tend to operate at slower speeds and thus are not ideal for applications such as peel testing. The larger, floor standing machines can weigh over 1,500 lbs. so proper planning must be undertaken for the shipping and final placement of the unit.
2. Settling in on a Suitable Controller
Control systems for Universal Testing Machines have evolved quite rapidly in recent years. Analog Vacuum Tubes and Paper Chart Recorders have been replaced with digital computers. Most UTM manufacturers offer two standard options for their controller units.
Standalone, Low-Feature Controller:
The standalone controller is ideal for highly repetitive testing such as in manufacturing quality labs. The interface has a pinpad and a small digital readout screen. Operators can select from a limited amount of tests and run the machine without a PC. Data is spit out on the screen and hand copied, or a series of raw data can be uploaded back to a PC for further analysis and documentation. These standalone type controllers tend to have less options in terms of servo-control, but they are also lower cost.
PC-Based, Full-Feature Controller:
PC-Based Controllers are more typically suited for R&D settings where operators are constantly making changes to their test procedures and doing advanced analysis on the data results. The machine is completely operated through the PC. The PC-Based controller can either be embedded inside a PC desktop tower, or can be embedded inside an external interface box. In some rare cases the controller and data acquisition (DAQ) is embedded in the base of the machine. USB and Ethernet are the two most common data connection types. Using this type of controller allows for much easier collection and management of data and test results, while also giving the user the maximum amount of control options. PC-based controller and software packages are generally more expensive than their standalone counterparts, however this is not always the case.
3. Identifying the Ideal Load Cell(s).
Over the years there have been many different types of devices used to measure load or force. The industry has settled in on strain gauge load cells. 4 individual strain gauges are typically wired in a Wheatstone bridge configuration which helps with stabilizing and calibrating the load cell(LC). These 4 strain gauges are packaged into a circular shell which is commonly known as a “pancake.”
As a rule of thumb, load cells work best between 5-95% of their posted range. If you have a 100 lb. load cell, it will not be able register very well below 5lbs. and a more sensitive load cell will be needed. The situation is slightly different at the higher end where the risk of damaging the load cell increases substantially as the load approaches the maximum capacity of the LC.
Hydraulic machines with high capacity will use a pressure gauge transducer or a similar type of sensor instead of a Load Cell. These pressure gauges are slightly different in principle, however they achieve the same result.
4. Grips, Fixtures, and Accessories
There are a myriad of grips and fixture options for Universal Testing Machines. The type of grip needed is based on the material constitution, sample geometry, and maximum anticipated force capacity. The Universal Grip Company offers the largest selection of grips in the world.
The majority of tensile testing applications will use either a vise grip or a mechanical wedge grip. Circular or square platens are used for compression testing. There are many more types of fixtures including bend test fixtures, puncture fixtures, and even special fixtures used to test food. Pneumatic grips are also popular because they help to standardize testing and increase throughput.
Aside from grips, there are many other add-ons including environmental chambers, extensometers, deflectomers, and sample preparation tools. The environmental chambers are also known as a furnace or test oven and can range in temperature from -70C to 350C, depending on the exact setup. Extensometers and deflectometers are used to measure elongation and compression and there are many types including regular contact, laser, and video extensometers.
Choosing the Best Supplier
UTM design and control theory is in a very mature state and the basic tenants of the machines are almost identical between suppliers. There are no longer any patents on these types of systems and the knowledge is now in the public domain. Universal testing machines tend to last for a very long time, and for that reason it is critical to choose a supplier that is easy to work with.
Some suppliers will use certain tactics in order to “lock-in” a customer. These tactics can include everything from holding calibration passwords ransom, to using unique adapter measurements which force customers to return for additional parts and services. Only the largest manufacturers use these tactics while the smaller players have chosen a strategy to develop their machines and controllers in a way that easily interfaces with 3rd party accessory components. 3rd party local calibrators are often employed to service and maintain UTMs for the smaller OEMs. UGC employs local calibrators to service and calibrate our machines.
Universal Grip has the engineering capacity to design adapter fixturing and mounts that will attach onto any machine.
Getting the Best Deal
The UTM industry is very old and there are many different suppliers. It is often difficult to identify exactly where the machine was manufactured since many brand names will use OEM suppliers. In recent years there has been an influx of machines and controllers manufactured in China and India. These machines are not necessarily poorly made, however it is difficult to find parts and support for these systems if a problem does arise. The good news is that there are many US-based OEMs who are willing to retrofit or re-condition these used machines. All testing machines from Galdabini are manufactured at their headquarters in Milan, Italy using high quality steel and electronic components.
The best way to get a good deal on a UTM is to do your research! Identifying your exact needs will help the conversation flow and empower you to make decisions based on your terms. Once you have honed in on a framework for your machine, you can start sourcing quotes. Pay careful attention to the support and service options as each supplier is slightly different.
We hope that you enjoyed this article! Savvy purchasing managers and engineers will realize that UGC distributes the same grips as many of the popular UTM manufacturers. Sourcing grips from UGC can extend overall testing budgets and allow for the purchasing of more equipment. We offer the best prices and delivery in the industry and our quality is top notch. Good luck with your new Universal Testing Machine!
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While many versions of testing systems were developed from 1850-1880, the design was not standardized and most manufacturing companies were tasked with building their own tester. According to the Tinius Olsen company, the first material testing system to unite both compression and tensile testing was the “Little Giant” which was developed by the Norwegian expat Olsen. Tinius gained his inspiration after working as a chief designer for the Riehle Brothers’ Philadelphia Scale and Testing Machine Works.