|Michigan Tech's Open Sustainability Technology Lab.|
Joshua M. Pearce
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|Cite as Adam Pringle, Joshua M. Pearce (2021). "CNC Router Parts-based metal printers SOP". Appropedia. Retrieved 2021-10-24.|
Safety checks must be carried out before any action when entering 329. Safety training is critical for continued lab usage and is a requirement of the department before access to the lab can be granted by the lab overseer.
Safety courses required[edit | edit source]
Baseline of knowledge needs to be guaranteed before anyone can be trusted with lab usage.
- 329 safety training - hazards
- MSE departmental safety training
- Gas cylinder safety training
- Welding safety training
Collection of personal protective equipment[edit | edit source]
PPE is to keep YOU safe so that you can keep doing what you want to do.
- Safety glasses – always required
- Welding helmet – required only if canvas cover not used
- Green jacket – required only if canvas cover not used
- Steel toes are highly suggested
- Natural fiber clothing is suggested
SDS and other[edit | edit source]
Knowing what chemicals are in the lab and how they interact with each other is critical when accidents happen.
- Appropriate SDS sheets should be viewed online.
- Note the hazards listed on the door to the lab. If you introduce any new equipment or materials you must clear them with the responsible person listed on the lab door. If the responsible person is out of date, contact the departmental administrators to get it updated.
Calibration & Tolerances[edit | edit source]
Printing Parameter determination[edit | edit source]
The printing parameters may either be well established for known systems, or require tuning depending on your application. Some key issues are highlighted below:
- Print parameters are coupled and difficult to optimize. Currently, the best guideline is a consistent sound, light intensity, and as uniform process as possible. Example parameters are shown in Table 1 .
- The CNC printer is only calibrated for aluminum alloys at this time – specifically 4047, and 6061. Other aluminum alloys may use the following parameters as a guideline, adjustments will be necessary.
- TBA Table 1: Metal additive suggested printing parameters
- Parameter Amount / Unit Range tested
- Welder power input (P) 14.5 V 14-18.5 V
- G-code layer height (LH) 1.25 mm 1 - 3.5 mm
- G-code line width (LW) 2 mm 1.5 - 4 mm
- G-code travel speed (TS) 30 mm/s 10 - 50 mm/s
- Tip standoff distance (SO) 9 mm 6 - 16 mm
- Nozzle geometry (NG) MIG (14 mm dia) 8 - 16 mm dia(poly)
- Wire feed rate (WFR) 5.25 mm/mm* 3.5-7.25 mm/mm*
- Gas flow rate (GFR) 40 CFH 25-60 CFH
- Water reservoir temp. (WT) 23 °C 13-25°C
- Substrate thickness(ST) 2.4 mm 1.6 – 6.2 mm
- Wire diameter(WD) 0.8 mm 0.8 – 0.9 mm
- EM lens current(LC) TBD 0 – 1.5 A
Printing Parameter determination[edit | edit source]
- Welder Power Output(P)
- The power output of the welder must be sufficiently high to consistently melt all wire mass as it is fed by the motor and maintain a stable plasma arc.
- Excessive power output may result in substrate burnthrough, critical loss of part dimensionality, porosity, nozzle blockage, and print failure.
- Low power output may result in lack of fusion, linear indications/cracks, and possible interrupted/inconsistent metal deposition.
- Tip standoff distance(SO)
- The standoff distance is distance in mm between the nozzle tip and the substrate or part underneath. This is set initially in Franklin by zeroing but must be consistent with every successive layer of the print for reliable results.
- G-code layer height(LH)
- The G-code layer height must be set after some initial testing at viable parameters. This is because as multiple layers are added the standoff (distance between the wire and work piece) needs to remain consistent. The degree of layer remelt should also be considered as this will influence the height variation throughout that must be accounted for during printing. This value is set in the G-code directly or in Cura.
- G-code line width(LW)
- The line width entered in Cura should be about 60-75% of the bead width as determined by single line test trials. At this size a relatively flat surface should be created, any larger and noticeable valleys and peaks form. A degree of surrounding deposition is expected to melt for bonding. This value is set in the G-code directly or in Cura.
- G-code travel speed(TS)
- The travel speed is referenced in the G-code with the notation of F, followed by a number. F1800 indicates a speed of 30mm/s. TS is important in relation to power output, mass flow rate, and gas flow rate to establish a stable plasma arc with good gas coverage efficiency.
- Nozzle geometry(NG)
- For a standard metal inert gas welder nozzle, it is 14mm. In combination with standoff distance and gas flow rate an effective gas coverage is achieved preventing contamination and reducing spatter and/or smut. A constant unless a polymer nozzle is used to test geometry effects.
- Wire feed rate(WFR)
- The wire feed rate is the extrusion amount referenced in the G-code and multiplied by the “wire” value in Franklin. Its best to get as close to a 1 mm per 1 mm relationship in G-code so that the extrusion value can easily be modified in Franklin for testing. There is an ideal value for WFR in combination with P and TS where a consistent and defect free deposition is achieved. Too much WFR will cause short circuiting and nozzle blockage, while too little will cause balling and poor deposition.
- Gas flow rate(GFR)
- The gas cylinder gauge used is in CFH(cubic feet per hour). The setpoint is reliant on the travel speed and stand off distance while considering the nozzle diameter. Faster travel will require more gas, higher stand off will require more gas to achieve the same gas coverage efficiency.
- Water reservoir temp.(WT)
- The water temperature controls the resting temperature of the copper chill plate. It is important for this value to not be too low(less than 16C) otherwise condensation has been observed on the copper chill plate. This value is only relevant if the chiller is in use. If the chiller is in use, then the part will cool significantly faster resulting in much different material properties.
- Substrate thickness(ST)
- The substrate thickness is important in relation to the P and TS parameters, as well as residual stresses generated. Thicker substrates will allow higher power levels while preventing burn through, and accommodating residual stress buildup.
- Wire Diameter(WD)
- Thinner wires allow for lower power input from the welder and faster travel speeds while maintaining a more stable plasma arc. Less wire allowing lower heat input also means a lower penetration into the substrate material and reliquification of previous material.
- EM lens current(LC)
- EM lens is a work in progress but would act as a replacement nozzle for printing. It would focus the plasma arc improving power density. Through melt pool stirring, porosity would be reduced, and solute uniformity would be increased.
[Physical prep] Room 329 lab space prep[edit | edit source]
- Gas cylinder
Gas cylinders are dangerous if used improperly and should be handled with care and respect.
- In general, argon gas with a purity of at least 99.995% should be used for aluminum printing to ensure minimal oxygen contamination.
- Ensure that the proper gas tank is hooked to the welder of choice.
- To switch out gas tanks:
- Use an adjustable wrench remove the regulator from the current gas tank and screw it onto the desired gas tank. Remember to tighten the regulator with the adjustable wrench to ensure no gas leakage.
- Remember to replace the safety cap on any gas tank not currently in use and ensure it is fastened to an appropriate wall mount. Do not store gas cylinders on transport carts.
- Take note of the gas line coming from the cylinder to the welder – move it from walkways and remove any kinks which could reduce gas flow or damage the lines.
- Fume hood controls
In some alloy/material combinations dangerous fumes may be created, when unsure, use the fume hood to protect yourself and others in the lab.
- During any fume hood usage, the light switch should be engaged
- The printer must remain within the fume hood at all times unless in repair or modification. The air flow must be turned on for the entirety of the printing session.
- Welder set up
Currently the Millermatic 215 is utilized for this metal gas arc welding process.
- Ensure the welder is off before proceeding with the next steps .
- Before use check the trigger, gas lines, electrode and grounding lines to ensure they are safe and will not engage immediately upon powering on the welder.
- Before use, the welding wire should be cut back from any grounded surface to remove the risk of circuit completion (shorting) and arcing.
- The gas line should be connected in the back of the welder, the electrode should be connected to the wire extrusion assembly, the ground should be connected to the substrate plate on the printer.
- Ensure welding gun electrode is properly attached to the base welder unit
- Insert the gun trigger plug(4 wire connector) into the welder’s appropriate receptacle and tighten.
- Locate the trigger switch by the wires connecting the toggle to the gun trigger plug and place in an easily accessible location for use during printing.
- Sensor circuit check
The sensor circuit allows the collection of data to improve the printing process.
- This section is unfinished and will eventually incorporate the “Arc Analyzer” circuit and sensors into the process in data gathering. Each sensor will be described later. Arduino IDE, Jupyter(python), and R Studio(R) code will be referenced in order to generate appropriate plots.
- Water cooling check
The chiller facilitates a measure of control over the temperature of the printing process.
- Check the water lines running from the cooler to the copper chill plate, looking for any standing water, or condensation.
- Ensure that the valve directing the flow of the water is turned to the printer to be used for experimentation.
Operation & Procedure[edit | edit source]
[Digital prep] Software prep[edit | edit source]
The following digital preparation should be completed before you enter the lab space.
Plan development[edit | edit source]
Decide on the end goals of the test/project to make sure this process works towards those goals.
- Check stock for desired wire alloy and substrate alloy compositions ideal for the part.
- Consider the material properties and dimensional requirements for the desired part.
- If working on a developmental alloy, identify comparable systems and investigate their welding characteristics. This will allow early weld parameter tuning and help predict potential issues.
G-Code generation[edit | edit source]
G-code is the direction list the printer uses to understand what you want it to do.
- G-code should be generated via the open sourced software Cura for complex designs (https://ultimaker.com/software/ultimaker-cura). Cura has many parameters, the most important ones are, travel speed, line width, layer height, and extrusion.
- Alternatively, if a simple geometry is needed G-code can be generated via notepad with simple G-code G0 X0 Y0 Z0, F, E, and G4 commands.
- After G-code is prepped it can be uploaded to Franklin, the firmware running the printer through a simple browse and select method .
- Example G-codes are shown below, commands can be looked up online for specific functions and added as necessary. The M42 P6 S255 or S0 lines toggle a specific relay tied to the activation circuit of the welder, so it necessary in any multi-layer print.
- TBA Figure 1: Example G-code for printing a single line 100mm in length, annotated for descriptions
- TBA Figure 2: Example G-code for printing a two layer 40 x 40 mm block with a line width of 2mm
[Lab operation] Printing process and operation[edit | edit source]
Consistency in operation is paramount for reliable results.
Substrate / nozzle Prep[edit | edit source]
- For printing aluminum, the substrate material suggested is a 6061 aluminum alloy (T6 or annealed is being investigated) between 2.4 and 3.2 mm in thickness (Z) and 150 x 150 mm (X-Y). Locate a substrate.
- As received, it has a built-up oxide layer and cutting fluid remnants which must be removed to allow effective electrical and thermal contact. To do this a circular belt sander is used on both sides of the substrate until a shinny surface is obtained.
- Place the substrate on the copper chill plate and stack the window frame on top of the substrate so it aligns with at least 3 holes drilled into the copper plate.
- Insert the grounding cable onto the same plane as the substrate so it makes physical contact.
- Hand screw in three points of contact securing the window frame to the substrate.
CNC Printer start-up and prep[edit | edit source]
- Turn on the printer by activating the power strip on the print table. This supplies power to the printer, as well as the sensor circuit, and laptop to run the printer.
- The laptop running the printer uses Linux and the username/password is reprap/reprap.
- After logging into the laptop, transfer the G-code for printing if necessary via a USB key and open the internet browser window. It has been modified to have the printer access terminal as the homepage as seen in figure 3.
- TBA Figure 3: Nominal Franklin interface.
- The browse button is used to upload G-code for Franklin to consider. Only have one file uploaded at once as Franklin is temperamental with multiple files.
- The current position of the nozzle is set as the 0,0,0 X-Y-Z position upon powering the printer.
- Use the position X-Y boxes to actively move the nozzle and position it at the desired starting location in the X-Y plane.
- Once the nozzle is in position transfer the X-Y values to the Target boxes and this will apply an additive modifier to the G-code values causing the print to start from that location.
- Ensure that there is no excess wire coming from the nozzle, then slowly lower the Z target position box until the nozzle is touching the substrate (lightly – piece of paper is a good tool here). Then increase the Target Z value by the determined stand off distance.
- Change the “wire” box value to 0.01, increase the Target Z value by 10, toggle the welder circuit trigger to the off position and click the “run selected job” button to do a dry test run. Reset values if successful and satisfactory.
Metal additive process operation[edit | edit source]
- The printer, G-code should be prepared and a dry run completed. Do not start the printer without a successful dry run as this will potentially damage the system (e.g. running the gun or print assembly into the work table)
- Input the appropriate multiplier value for “wire” to reach the desired extrusion rate .
- Set the wire stick out length to be about 2-3mm by extruding wire in franklin. This is important so that the wire does not jam in the tip during arc ignition.
- Press the abort and home buttons in order to reset the wire extruded values and prepare the Franklin Firmware for testing.
- Turn the gas cylinder to the desired gas flow rate.
- Turn on the chiller if desired.
- Power on the welder and verify the power setting is appropriate.
- Toggle the welder circuit trigger to on.
- Turn on the fume hood air flow
- Press the run selected job button to begin the test.
- Change the Target X-Y values to modify the start position of successive tests on the same substrate if desired.
Shutdown[edit | edit source]
[Lab shutdown] Cooldown[edit | edit source]
- Remove substrate
- Turn off gas
- Turn off fume hood
- Turn off light
- Turn off sensor equipment
- Turn off welder
- Turn off CNC printer